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Siguy
2008-Nov-15, 09:52 PM
I personally am vehemently against a manned moon mission before a Mars mission or moon colonization mission. This has been further enforced by what I just heard- NASA will spend about ONE HUNDRED BILLION on it. That is insane. I know that NASA missions are always really excellent even if they are bit expensive, but this would make it the most expensive mission since the original moon landings, and by that I mean the cost of the entire Apollo program. I mean, we developed the technology before, why should it cost as much or more to do it again?

Considering that Scaled could probably put a man on the moon for a couple billion, perhaps much less, why should it even be NASA's job to return? A government space agency's goal is to open new frontiers, after that, leave it to private aerospace companies.

Don't think that I'm a NASA hater. I love NASA, the Mars rovers, the Cassini spacecraft, etc. are all so wonderful. But sometimes they don't spend their budget wisely.

Also, do not think that I don't want a hundred billion to be spent in space. I would love that, but it would be a total waste to spend it on the moon. If they would use it to build a Lofstrom/Launch loop, or something of that sort, that would be absolutely fantastic, because that's exactly what we need. Or it could be spent in research. Just imagine, 10 billion, let alone a hundred billion, could almost certainly find a solution to interstellar/FTL travel.

If they spent this kind of money on a mission to Mars, I'd be fine. But there simply isn't justification in going to the moon.

Nicolas
2008-Nov-15, 10:27 PM
Considering that Scaled could probably put a man on the moon for a couple billion

On what do you base that statement; what makes you assume that Scaled could put a man on the moon at all?

If we want to colonize the moon, we'd have to develop a good way to get there first. That's exactly what NASA wants to do now. In the 60's and 70's we went to the moon. Now we want to go there in a more decent way. Next step: stay there. Next step: Mars. One thing at a time. Otherwise, we might end up making something that just barely gets people to Mars, not to return for another 50 years. It may be better to do things in a more developed, less experimental (with all respect for Apollo hardware, but it couldn't be called the ultimate suitable-for-all no-brainer way to get to the moon) way this time.

PraedSt
2008-Nov-15, 10:43 PM
No, NASA often don't spend their budget wisely. But that's not really their fault- it's not a homogeneous institution, they have many 'parts', and all need a share of the overall budget.

Second, going back to the Moon is still as much of a frontier as it ever was. It's not easy!

Third, I am a huge fan of private sector involvement in space, but I'm also a business man and investor. From my perspective, it's far to early in the game to invest in Lunar transport. So far, we've had 2 suborbital flights, by one company. That's it.

Lastly, you seem to be ok with a Mars mission and Lunar colonisation. Well, this is the way to do it I think.

:)

cjl
2008-Nov-15, 11:00 PM
What makes you think that Scaled could put someone on the moon for a couple billion? They have yet to even make it to orbit.

Siguy
2008-Nov-15, 11:08 PM
On what do you base that statement; what makes you assume that Scaled could put a man on the moon at all?

The cost of the entire SpaceShipOne project I think was about $25 million. That is research, development, planning, construction, flights, everything. Next year SpaceShipTwo will debut. It's costing a lot more, but that's because it will be carrying wealthy passengers in considerable luxury. That's a five year gap between models. SS3 will almost certainly be orbital, presumably able to dock with the ISS, and is likely to cost very little and be developed quickly when compared to say, the Orion. The next logical step would be a spacecraft capable of leaving Earth orbit, and could happen by 2020 depending on how well SS2 goes.

Private companies have a lot of motivation. They can develop new spacecraft quickly and cheaply. Scaled/Virgin isn't the only endeavor, there are plenty of other companies catching up. They have made the most progress so far, however.

PraedSt
2008-Nov-15, 11:15 PM
Private companies have a lot of motivation. They can develop new spacecraft quickly and cheaply. Scaled/Virgin isn't the only endeavor, there are plenty of other companies catching up. They have made the most progress so far, however.
This is true Siguy. The motivation is profit though, and profit from lunar transport won't be so easy to come by without first completing many other profitable steps beforehand.
Look, I don't think you're far wrong. It's just that I think you're being a trifle optimistic with your private sector time-line, that's all.

cjameshuff
2008-Nov-15, 11:33 PM
Scaled Composites, while they make some neat aircraft, has no experience in spaceflight. You would be better off with a company like SpaceX, which has actually put hardware of their own into orbit. But yeah, looking at NASA's plans, I get the unsettling feeling we'll end up with another horribly expensive launch system that requires enormous manpower to use and lots of money spread across the usual voting districts and contractors to build. I have some doubts about the ability of a small company like SpaceX to feasibly grow fast enough to handle a moon landing in the timeframe involved, though.

I do wonder sometimes about splitting off manned spaceflight to a separate agency, but then worry about the far less pathological parts of the agency that handle the robotic science missions getting cut down to nothing while funding focuses on the new agency. Contracting entire vehicles and launch systems out to one or two companies might be a better approach.

I definitely support going to the moon if we're developing the infrastructure to stay. People arguing for the Mars first option seem to be pushing for another "touch down and then go back home for a half century" mission. The moon missions shouldn't be a dry run for a Mars-and-back mission, they should be a permanent expansion of our capabilities in space.

Siguy
2008-Nov-16, 12:22 AM
Sure, Scaled is inexperienced, but they have a huge advantage compared to other spaceflight companies in that they're backed by a billionaire and a giant multinational corporation.

Also, while the Orion is "meh", the SpaceShipTwo just speaks awesome. It's clean and efficient, and being designed by Burt Rutan, looks beautiful. You have to agree that this (http://www.youtube.com/watch?v=WBo8t0B5NhM) is really, really cool. Shame about those cheesy spacesuits. That's a real deal killer. :P

cjameshuff
2008-Nov-16, 12:45 AM
Also, while the Orion is "meh", the SpaceShipTwo just speaks awesome. It's clean and efficient, and being designed by Burt Rutan, looks beautiful. You have to agree that this (http://www.youtube.com/watch?v=WBo8t0B5NhM) is really, really cool. Shame about those cheesy spacesuits. That's a real deal killer. :P

It's cool, but it's an airplane. The SpaceX Dragon isn't going to the moon, but it's a lot closer to something that could.

Siguy
2008-Nov-16, 01:16 AM
It's cool, but it's an airplane. The SpaceX Dragon isn't going to the moon, but it's a lot closer to something that could.
Yes, that is a very practical spacecraft, sort of like a mini-Orion. That will certainly have its place, perhaps even leading to an interplanetary spacecraft. But I still think that Scaled is close to developing a fully reusable orbital spaceplane. I'm not saying a spaceplane could get us to the moon, but it's a cheap way to get into orbit, and therefore useful for developing infrastructure. A future private spacestation could serve as a dock for building or refueling a lunar or interplanetary spacecraft, which would then make the entire system reusable.

I really think that orbital spaceplanes will eventually serve as transit between space stations and Earth.

But for actually building those space stations, a launch loop is what we totally need, and the only budget that could afford that would be a government budget, which is one of my main points against a NASA moon mission: if we are planning on spending tens of billions of dollars in space, we should spend it on the thing that gives the most in return. That would either be interstellar travel research, or a launch loop. I cannot stress enough that these are the two things we need most.

novaderrik
2008-Nov-16, 06:19 AM
Also, do not think that I don't want a hundred billion to be spent in space. I would love that, but it would be a total waste to spend it on the moon. If they would use it to build a Lofstrom/Launch loop, or something of that sort, that would be absolutely fantastic, because that's exactly what we need. Or it could be spent in research. Just imagine, 10 billion, let alone a hundred billion, could almost certainly find a solution to interstellar/FTL travel.

i might be a bit on the naive side, but isn't that the whole stated purpose of going to the moon again- to do research on ways of not only getting to Mars, but keeping the crew alive for the journey there and back again?
NASA does the best they can with what they've got- they have resources that no private company has access to and they aren't motivated by profit, so they try out things before anyone else does.
NASA is where the best and brightest go- even if they could make more money elsewhere. what scientist or aerospace engineer wouldn't want to have NASA on their resume?
the only real problem i can see with NASA is that they are totally dependent on the whims of the current leadership- we have three more national election cycles (2 congressional and one presidential) before the new launch system is due to start lobbing people into LEO, and a couple more election cycles before they are scheduled to send people towards the moon. that is a LOT of time for the enthusiasm of the leadership of this country to decide that they'd rather send the money elsewhere.

Nicolas
2008-Nov-16, 10:58 AM
Next year SpaceShipTwo will debut. It's costing a lot more, but that's because it will be carrying wealthy passengers in considerable luxury.


Is it? Me thinks it's more expensive because it is larger and needs to be more reliable. Fancy seats and carpets will not drive the cost up that much.



SS3 will almost certainly be orbital, presumably able to dock with the ISS

Will it? When?



and is likely to cost very little and be developed quickly when compared to say, the Orion

Will it? And if so, can you really compare the two?



The next logical step would be a spacecraft capable of leaving Earth orbit, and could happen by 2020 depending on how well SS2 goes.

And that timeframe is based on?



Scaled/Virgin isn't the only endeavor, there are plenty of other companies catching up. They have made the most progress so far, however.

But they've put nothing in orbit, others have (SpaceX). And you want to go to Mars.


Also, while the Orion is "meh", the SpaceShipTwo just speaks awesome.
Your "meh" can travel to the moon and back, your "awesome" basically farts itself a little bit upwards and immediately falls back. It's all a matter of perception...


It's clean and efficient, and being designed by Burt Rutan, looks beautiful.
If it takes a pile-of-vomit lookalike ship to get us to mars, I'd be the first in line to yell "godspeed you beauty" at the launch. That is, unless I'm allowed to fly in it, in which case I'd be yelling "show us what you've got, beauty" from the cockpit. Beautiful is not of any importance when going to the moon or mars. You could even consider it as a waste of resources. It's only important when you're going on the commercial passenger service market. The LEM was so ugly that it was charming. To me, at least.



Yes, that is a very practical spacecraft, sort of like a mini-Orion. That will certainly have its place, perhaps even leading to an interplanetary spacecraft.

Will it?



But I still think that Scaled is close to developing a fully reusable orbital spaceplane.

Are they?



I'm not saying a spaceplane could get us to the moon, but it's a cheap way to get into orbit, and therefore useful for developing infrastructure.

Such as the STS?



A future private spacestation could serve as a dock for building or refueling a lunar or interplanetary spacecraft, which would then make the entire system reusable.

The fact that it's private or governmental doesn't really matter for its functionality.



But for actually building those space stations, a launch loop is what we totally need, and the only budget that could afford that would be a government budget, which is one of my main points against a NASA moon mission: if we are planning on spending tens of billions of dollars in space, we should spend it on the thing that gives the most in return. That would either be interstellar travel research, or a launch loop. I cannot stress enough that these are the two things we need most.

You don't allow them to develop something that takes us to the moon in a decent way, yet they should pump money into interstellar travel? :confused:

About that launch loop: yes, it's important. NASA knows. They've got some experience with launching stuff. Both in the throw-away and reusable variant. Turns out that with the current state of technology, a fully reusable space plane is still a bit of a stretch both on budget and technical possibilities. Throw away is relatively cheap, and for Ares, they do incorporate reusable aspects into the capsule concept. It doesn't have to have wings to be good or cheap. One could say that NASA is showing a pragmatic approach normally only seen in the private sector by not going for a fully reusable space plane.

Now I'm not trying just to get at you. But not everything that private companies do is good, cheap, fast. Not everything that governments do is bad or a waste of money. And just as your "launch loop" is so important, a "moon loop" is important for the lunar colonisation you want. Orion is a good step in developing such a "moon loop". As for interstellar: don't hold your breath. Look at how long it takes for Orion to get merely to Pluto, and that is the fastest thing we've ever thrown off our planet.

cjameshuff
2008-Nov-16, 04:23 PM
It is a mystery to me how adding useless wings and the heat management systems and physical structure needed to plow through atmosphere at hypersonic velocities for an extended amount of time will get you to orbit cheaper. Spaceplanes are "cool", but they aren't even remotely describable as cheap or efficient.

As for launch loops and other advanced launch concepts like mass drivers...the moon is an ideal environment for testing out such things, due to the lack of atmosphere and shallower gravity well. Once they're in place, simple materials like nickel-iron, basalt fiber, and plain old moon-dirt could be cheaply delivered into orbit for the purpose of constructing and shielding space facilities.

PraedSt
2008-Nov-16, 04:50 PM
It is a mystery to me how adding useless wings and the heat management systems and physical structure needed to plow through atmosphere at hypersonic velocities for an extended amount of time will get you to orbit cheaper. Spaceplanes are "cool", but they aren't even remotely describable as cheap or efficient.
Heh. One of my many failings is an inexplicable fascination with SSTO. As far as I'm aware, (I haven't followed up in a while), the three main advantages over conventional methods are:
1. Less reaction mass
2. Less oxidiser
3. Less gravity drag

But yes, on the other side of the scale, are a ton of disadvantages, some of which you mention. But I'm still fascinated. :)

cjameshuff
2008-Nov-16, 06:06 PM
1. Less reaction mass

Not true...you just get some of it from the atmosphere. And it's already moving at hypersonic speeds in the direction you're trying to accelerate it in, making it rather difficult to use for the purpose of producing thrust.



2. Less oxidiser

But if you're air-breathing, you need LH2 fuel...nothing else burns fast enough. LH2 is more expensive and harder to work with than LOX. And very low density...you need a monstrously huge deeply-cryogenic fuel tank. And you still need the LOX tank to get you up to orbital velocity once you finally leave the atmosphere, just a somewhat smaller one. Are you sure reducing its size is really that helpful?



3. Less gravity drag

You're climbing up an inclined plane over a much longer period of time. I wouldn't expect gravity drag to be that much lower, and aerodynamic drag at hypersonic velocities is...significant.

PraedSt
2008-Nov-16, 06:14 PM
Your points seem valid to me. I doubt you'll convince the SSTO people though. They're a bit like the gold bugs in my field. :)

Nicolas
2008-Nov-16, 06:17 PM
about the "less reaction mass" and "less gravity drag": with multi-stage, you have a lighter ship once you've dropped the first stage(s), so I'm not sure the advantage would be with the SSTO craft.

The one advantage I see for SSTO is that you need to take care of only one piece. Which can be important when the craft is reusable (so it matters what happens to the pieces) and you go into space really often (otherwise it's no burden to take care of all stages). So, SSTO may be nice once we get towards space flight similar to what air traffic was in the 50's.

Air breathing can be very interesting, but it can also be applied as a first stage of a multi-stage craft. The same can be said about wings, although I consider them less interesting during ascent, rather a burden.

In short: you can have wings and air-breathing also without SSTO, and I see very very little use of SSTO in the current state of affairs of space flight.

I'd be happy to hear good arguments pro SSTO.

Siguy
2008-Nov-16, 06:36 PM
Is it? Me thinks it's more expensive because it is larger and needs to be more reliable. Fancy seats and carpets will not drive the cost up that much.

Well, yes, that's what really drives the cost up, and that's what I was what I meant by the fact that it's carrying passengers. I don't think it has carpets, but those seats must cost at least $100K each!

Will it? When?

http://www.space.com/news/060811_rutan_interview.html
http://www.flightglobal.com/articles/2005/08/23/201097/spaceshipthree-poised-to-follow-if-ss2-succeeds.html
http://www.space-tourism.ws/spaceshipthree.htm
Rutan also briefly mentions going to the moon in the first one.


Will it? And if so, can you really compare the two?

And that timeframe is based on?

I'm not comparing them as spacecraft, but in development times. Orion's development will take 10 years from announcement to first flight. SS2, if everything goes right next year, will have taken five years from announcement to first flight.


But they've put nothing in orbit, others have (SpaceX). And you want to go to Mars.
Once again, I'm not saying they'll get us to Mars. I'm saying that Scaled's reusable spaceplanes will probably play a role in the future of getting to orbit, cheap.


Your "meh" can travel to the moon and back, your "awesome" basically farts itself a little bit upwards and immediately falls back. It's all a matter of perception...

If it takes a pile-of-vomit lookalike ship to get us to mars, I'd be the first in line to yell "godspeed you beauty" at the launch. That is, unless I'm allowed to fly in it, in which case I'd be yelling "show us what you've got, beauty" from the cockpit. Beautiful is not of any importance when going to the moon or mars. You could even consider it as a waste of resources. It's only important when you're going on the commercial passenger service market. The LEM was so ugly that it was charming. To me, at least.

I'll admit that what I said was a bit childish, and beauty and aerodynamics have no importance in interplanetary travel, in fact, I don't think a spaceship should look like a plane. I think that spaceships should mainly be reusable, however, and that's one of the reasons I'm using Scaled as an example.

Will it?
It looks pretty credible.

Are they?
I think so.


Such as the STS?

...Which costs $450 million per launch.

The fact that it's private or governmental doesn't really matter for its functionality.
True.


You don't allow them to develop something that takes us to the moon in a decent way, yet they should pump money into interstellar travel? :confused:
Which would still have benefit in interplanetary travel, and part of the research would help other aspects. Personally, I think we need to get out of this planet to ensure our survival, soon. If we made a breakthrough, that would certainly motivate the construction of some big space infrastructure.


About that launch loop: yes, it's important. NASA knows. They've got some experience with launching stuff. Both in the throw-away and reusable variant. Turns out that with the current state of technology, a fully reusable space plane is still a bit of a stretch both on budget and technical possibilities. Throw away is relatively cheap, and for Ares, they do incorporate reusable aspects into the capsule concept. It doesn't have to have wings to be good or cheap. One could say that NASA is showing a pragmatic approach normally only seen in the private sector by not going for a fully reusable space plane.

Now I'm not trying just to get at you. But not everything that private companies do is good, cheap, fast. Not everything that governments do is bad or a waste of money. And just as your "launch loop" is so important, a "moon loop" is important for the lunar colonisation you want. Orion is a good step in developing such a "moon loop". As for interstellar: don't hold your breath. Look at how long it takes for Orion to get merely to Pluto, and that is the fastest thing we've ever thrown off our planet.
Yes, you are right about private vs. government. But private can do a lot, and it has done a lot so far.

I would say that the launch loop would be more important, because it would be the start of a "moon loop".

PraedSt
2008-Nov-16, 06:41 PM
I'd be happy to hear good arguments pro SSTO.
I can only give you an end-user's point of view. If one of you scientists/engineers can build one, I'd fly it!

My reasons are partly psychological, partly cultural. It's gotten to the stage where it just seems a more natural way of doing things. We're habituated to travelling in vehicles that stay in one piece. We don't like bits falling off them! And, whether this is eventually true or not, it seems at first glance that a single-piece vehicle would be easier, and cheaper to maintain.

I suspect that the market for an SSTO spacecraft might be larger than what one would expect, given our cultural, social, and transportation history.

I would like to have something clarified though. Do the laws of physics completely rule out SSTO? Or is it simply a very poor alternative to current methods?

Nicolas
2008-Nov-16, 08:14 PM
We're habituated to travelling in vehicles that stay in one piece.

I see, you've never bought a French car. ;) :D

You've got a point about end-user perception. But I think that in that case, it's time to change that perception. Just like the ultra-ugly LEM, spacecraft at this time in history need to do what they do as good as possible. If we get in the future to the stage where there's room for improvisation in appearance, we can go down that road.

But just to put things into perspective: aircraft hardly are at a stage where we can go wild on appearance. They are meant to fly safe and efficient in the first place. We can play around with paint schemes a bit and do our best to make the windows larger, but that's it. Look at the 787's shark tail: a minor variant on the real 787, but it would have meant a decrease in efficiency, so they went for the better but more ugle "regular" tail. Now look at spaceflight: the STS ET is not painted white but remains ugly rusty brown to increase efficiency (less useless mass). That is the stage spaceflight is in regarding room for appearance issues...

cjameshuff
2008-Nov-16, 08:31 PM
I would like to have something clarified though. Do the laws of physics completely rule out SSTO? Or is it simply a very poor alternative to current methods?

They barely allow it. It's just less efficient, and likely fundamentally more dangerous. The vehicle to lift a given cargo must be huge, and with very little structural margin. I find the combination of razor thin margins and vehicle reuse particularly unappealing. I suspect the economics of a two-stage launch will keep that as the option of choice, though we'll likely throw a lot of money away trying to make SSTO practical.

Aside from the opportunity to drop a lot of unneeded engine, tank, and structure mass, a launch very naturally divides into two different stages. Early on, you need a lot more thrust than you do in later flight, because you're both lifting more fuel and trying to get out of the atmosphere and to orbital velocity, minimizing time spent "hovering" against gravity. Engines are optimized for operation in atmosphere or for vacuum...you can make an engine that can adapt, but it will never perform as well as a specialized one. The second stage also needn't carry protection against supersonic airflow or present an aerodynamically clean profile if the separation is made high enough and it isn't destined to return intact. A first stage, on the other hand, is relatively easy to protect for reentry, as it does so at far less than orbital velocity. If you carry it all the way into orbit, you need to drag along even more thermal protection in order to have it reenter and be reused.

And if you're lifting large amounts of material into orbit that's going to stay there, why drag along an entire vehicle that's capable of reentering? You'll just end up making many launches with smaller payloads than you're technologically capable of lifting, wearing out your reusable launch vehicle, increasing chances for a failure, and spending a lot more money. The SpaceX approach of reusing the first stage and using a disposable second stage just makes sense.

timb
2008-Nov-16, 11:24 PM
Is the hypersonic aeroplane concept of any use as the first stage? If it could lift the detachable space module (2nd stage) to, say, 60km at mach 9, it would have pretty much have done the work of a first stage.

slang
2008-Nov-16, 11:40 PM
The cost of the entire SpaceShipOne project I think was about $25 million. That is research, development, planning, construction, flights, everything.

Compare that to cost of the development and flight of the first X-15 (http://en.wikipedia.org/wiki/X-15), not Apollo and everything preceding it. That might give a realistic comparison (obviously with the caveat that the whole flight regime of the X-15 was unexplored back then). I would post the X-15 project cost here but I don't have the numbers, sorry.

Siguy
2008-Nov-17, 01:00 AM
Compare that to cost of the development and flight of the first X-15 (http://en.wikipedia.org/wiki/X-15), not Apollo and everything preceding it. That might give a realistic comparison (obviously with the caveat that the whole flight regime of the X-15 was unexplored back then). I would post the X-15 project cost here but I don't have the numbers, sorry.
http://www.thespacereview.com/article/204/1

Ilya
2008-Nov-17, 01:58 AM
Your points seem valid to me. I doubt you'll convince the SSTO people though. They're a bit like the gold bugs in my field. :)

Are you an economist? :)

Oh, and to answer the OP: No, it is not at all certain. In fact, given the events that transpired since President Bush announced Vision for Space Exploration, I find it not even very likely.

PraedSt
2008-Nov-17, 07:22 AM
Are you an economist? :)

Oh, and to answer the OP: No, it is not at all certain. In fact, given the events that transpired since President Bush announced Vision for Space Exploration, I find it not even very likely.
An economist only by training, thankfully. :)

And, have I understood you correctly? You think we're not going to the moon? You referring to the problems with Ares?

slang
2008-Nov-17, 07:58 AM
http://www.thespacereview.com/article/204/1

Thanks for the link.

PraedSt
2008-Nov-17, 08:57 AM
I see, you've never bought a French car...

They barely allow it. It's just less efficient, and likely fundamentally more dangerous...
Lol! I remember the 2CV. A most amusing car. :D

Thanks for that cjameshuff. It might be a bad thing that physics doesn't completely rule out the spaceplane, (leaving aside my wants for the moment). As long as there's a glimmer of hope, I think designers will keep coming back to it.

An article once explained to me the conceptual reasons behind spaceplanes. Now, it was a long time ago, and I'm not even sure if I understood it then, but here goes:

The author used that school textbook problem of a lifeguard having to rescue a swimmer who's not directly in front of him. The trick is to find the path that takes the shortest time, and this path is the one between the direct one (too much water) and the totally indirect one (too much distance). Everyone remember that?

Anyway, his point was that 'horizontal' velocity is the primary goal of getting to orbit (obviously). The best way then, would be to acquire all of this velocity by flying horizontally 1 metre off the ground. But gravity and aerodynamic drag rule this out. Current methods get round this by going straight up, and then, once out of the atmosphere and sufficient velocity has been built up, keeling over to the horizontal.

His contention was that there's a happy medium- a flatter trajectory. At low velocities, air helps you to accelerate. At higher velocities the air becomes a hindrance. So a spaceplane is supposed to take advantage of this, using the atmosphere up until the point where it's disadvantages begin to outweigh it's advantages. Then, having timed it's trajectory and acceleration, that the spaceplane 'emerges' from the atmosphere and switches to 'pure rocket mode'.

Did that make sense? Or maybe I didn't understand the author correctly? :)

Nicolas
2008-Nov-17, 09:17 AM
That makes sense. However, traditional curved rocket launches also make sense: you go out of the thick atmosphere as soon as possible (straight up), and once you're outside the area that would give most resistance to it, you start building your horizontal speed while further gaining altitude. Doesn't sound bad eh. :)

Nicolas
2008-Nov-17, 09:23 AM
Is the hypersonic aeroplane concept of any use as the first stage? If it could lift the detachable space module (2nd stage) to, say, 60km at mach 9, it would have pretty much have done the work of a first stage.

Yes, but they are not looking that much into planes as first stages, just the engines. Space agency scramjet engine research focuses both on hypersonic passenger/military planes as air breathing first stage or boosters engines. I haven't heard about hypersonic "first stage" planes research lately.

An issue with scramjet engines is their need for a large velocity before they work. there's a range of possibilities to get around that. Simple one: make scramjet boosters that only kick in once the stack reaches say mach 2. Alternative: use start rockets inside the scramjet and have them work from the beginning. There's more possibilities.

The question to ask is whether they have an advantage over just using rockets, both in the sense of added weight or their ability to only start working at a speed that is reached when we've already had quite a bit of atmosphere behind us.

But hey, that's what research is for. Apparently it was not a clear "no", as they are seriously investigating the possibility of scramjet (booster) stages for launch vehicles.

timb
2008-Nov-17, 10:12 AM
Yes, but they are not looking that much into planes as first stages, just the engines.


That'd be the extremely cut-down hypersonic plane. Would it also have wings that would be jettisoned? or would the scramjets be more like strapon boosters on a conventional rocket?



Space agency scramjet engine research focuses both on hypersonic passenger/military planes as air breathing first stage or boosters engines. I haven't heard about hypersonic "first stage" planes research lately.

An issue with scramjet engines is their need for a large velocity before they work. there's a range of possibilities to get around that. Simple one: make scramjet boosters that only kick in once the stack reaches say mach 2. Alternative: use start rockets inside the scramjet and have them work from the beginning. There's more possibilities.

The question to ask is whether they have an advantage over just using rockets, both in the sense of added weight or their ability to only start working at a speed that is reached when we've already had quite a bit of atmosphere behind us.


Yes, that's what I was asking: are they a win compared to a rocket first stage? Given scramjets' problems at low velocity, they could be seen as a second stage in a three stage to orbit (3STO) solution.


But hey, that's what research is for. Apparently it was not a clear "no", as they are seriously investigating the possibility of scramjet (booster) stages for launch vehicles.

Let's hope something good comes of it. People say it was obvious the space shuttle was an inferior solution, but it didn't stop them spending a great deal of money on it.

Nicolas
2008-Nov-17, 10:28 AM
That'd be the extremely cut-down hypersonic plane. Would it also have wings that would be jettisoned? or would the scramjets be more like strapon boosters on a conventional rocket?

What I've seen was very conceptual, but were wingless vertical things, such as strap-on boosters. Haven't seen anything on horizontal (winged) launch things lately. Of course I don't or didn't get to see everything :).


Yes, that's what I was asking: are they a win compared to a rocket first stage? Given scramjets' problems at low velocity, they could be seen as a second stage in a three stage to orbit (3STO) solution.
That's the main research question (apart from fundamental scramjet engine research of course, first we'd have to make these things before we'd apply them :)): do scramjets offer an advantage during launch; if so where and how during the launch sequence do they fit in best? Last thing I know, they were still trying to answer these questions. And as we learn more about prtactical scramjet engines, we'll have to readjust these answers.

Ilya
2008-Nov-17, 01:22 PM
An economist only by training, thankfully. :)

And, have I understood you correctly? You think we're not going to the moon? You referring to the problems with Ares?
Mostly problems with Ares, but not entirely. Also politics.

cjameshuff
2008-Nov-17, 02:59 PM
Given that scramjets don't function at sea level or subsonic velocity or outside the atmosphere, and so will not run for long in a vertical launch, and the fact that they probably won't produce enough thrust to lift themselves vertically, and certainly won't come near the thrust to weight of a chemical rocket, implies they won't be much help. Scramjets are mostly useful in horizontal cruise flight, not vertical acceleration. And for that, given the difference between the velocity required for orbit and that achievable in atmospheric flight, and the need for structure and thermal protection for an extended flight at hypersonic speeds, and the limitations on fuel you can use (bulky, expensive, hard to handle LH2's the only thing that works)...I come back to this question: why, exactly, are you trying so hard to reduce the amount of LOX used? It is tricky stuff to handle safely, but we've got quite a bit of experience with doing so and have proven that we can use it in large vehicles. It's also very cheap and can be produced on location, and in terms of temperature is no harder to handle than liquid nitrogen, not at all like 20K LH2.

Scramjets are an interesting technology, but I don't see them being useful for anything but cruise missiles and hypersonic bombers. Technically, commercial flight could use them, but the record of such things is not promising. Actually, commercial flight would probably be better off using suborbital hops on LOX/RP1 or hybrid fueled vehicles. Military applications benefit from staying below the horizon as long as possible.

Nicolas
2008-Nov-17, 03:12 PM
Quite some current rockets also use huge tanks of LH2 (53,488 cubic feet for the STS), so that in itself is not an argument. And scramjets appear to be able to generate a lot of thrust. The remaining question is whether their added weight and possibly reduced thrust compared to rocket engines saves their gain in not needing to bring as much LOX. Further research will learn.

Why wouldn't they work at sea level? You're right that they don't work at low velocities.

PraedSt
2008-Nov-17, 03:52 PM
I think I'm going to annoy everybody and start a 'Spaceplane Updates' thread :D

cjameshuff
2008-Nov-17, 04:04 PM
Quite some current rockets also use huge tanks of LH2 (53,488 cubic feet for the STS), so that in itself is not an argument.

The STS does indeed use LH2. I fail to see how that invalidates my argument. ;)

Some other rockets use it for upper stages where the higher Isp is of greater importance. The Delta IV and Ariane 5 use it for the first stage, and they are huge and expensive vehicles. They are better counterexamples to my argument, though they also illustrate the massive increase in size required for hydrogen fuel, something that's less important for a rocket that exits the atmosphere early on than it is for an air-breathing hypersonic aircraft. Most rockets use LOX/kerosene or nitrogen tetroxide/hydrazine.



And scramjets appear to be able to generate a lot of thrust. The remaining question is whether their added weight and possibly reduced thrust compared to rocket engines saves their gain in not needing to bring as much LOX. Further research will learn.

Scramjets can produce thrust at high airspeeds. I've not seen anything that indicates they can produce particularly high amounts of thrust. In fact, estimates I've seen are for a thrust to weight ratio a couple orders of magnitude lower than that of chemical rockets, with the main question being whether thrust can exceed drag and thus actually accelerate.



Why wouldn't they work at sea level? You're right that they don't work at low velocities.

They might technically work at sea level, but surviving hypersonic flight at that altitude is another issue. Everything I've seen indicates that real scramjets will have a minimum altitude below which heating and aerodynamic stresses are unsurvivable. Of course, for launch, the problem is in reaching operating speed before exceeding the maximum operating altitude...and spending enough time in that range to get a benefit from a low-thrust scramjet.

Nicolas
2008-Nov-17, 04:11 PM
Now that you've clarified your statements, I understand your points and largely agree with them.

Personally, I can see a possibility for scramjet rocket boosters, but I'm not holding my breath. I wouldn't be surprised at all if research shows they're quite pointless for that purpose. Even for aircraft propulsion, it's no easy task, and that is a flight regime that a scramjet should love...

Next-gen scramjets (yes, we're already designing next-gen while first-gen hasn't really flown yet :)) scramjets are a bit better in the T/W department than current designs though, so maybe... We'll have to wait and see.

Nicolas
2008-Nov-17, 04:12 PM
I think I'm going to annoy everybody and start a 'Spaceplane Updates' thread :D

You may have a point there...:whistle: