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jokergirl
2009-Aug-27, 05:06 PM
I got into an interesting discussion with a friend before and was wondering what you guys think:
"Would it be worth while to lift rockets up by balloons and fire them from there?"

I personally think that the payload of a balloon is pretty low, so it'd be hard to do - and I don't know how you would protect the balloon/zeppelin once you are firing (unless you don't care about reusing). I'm thinking about clusters, but the payload of those is even lower. His argument is that the rocket would not need as much fuel, so it would be lighter, which might make it worthwhile again if you calculate the cost of balloon vs. cost of fuel.
Then there's the whole impossibility of calculating a trajectory from something that floats in random air currents...

Got anything to add?

;)

Swift
2009-Aug-27, 05:16 PM
If you want to achieve orbit, you still have to achieve the same velocity and launching from the height of the balloon gives you little advantage - at least that's my understanding.

KaiYeves
2009-Aug-27, 05:27 PM
There are some sounding rockets that work like this.

Drbuzz0
2009-Aug-27, 05:39 PM
I personally think that the payload of a balloon is pretty low, so it'd be hard to do - and I don't know how you would protect the balloon/zeppelin once you are firing (unless you don't care about reusing).

There are weather/research balloons that can lift a good couple of tons to a high altitude. They're generally not something that gets reused because they're made out of a very thin material that is not durable enough to last more than a single use.

There would be some savings in terms of fuel used to achieve altitude, because raising any mass to a higher altitude does take some energy, but that's a fairly small portion of the energy used to go into orbit. It's really the velocity that the fuel is expended on.

Still, there would be a couple of advantages worth considering. For one thing, the rocket would not have to contend with low altitude wind resistance. A bigger thing is that the rocket engine design could be optimized for altitude and vacuum operation without sacrificing launch effeciency. This is always an issue with sea level launches: the engine bell design. An engine that achieves the best effeciency at sea level will have a lower effeciency at high altitudes or vice-verse. There is always some level of compromise on this and it's why aerospike engines have been considered because they can compensate for this.

It might be better to consider launching from an airplane. That is how Orbital Systems Pegasus is launched. There are some logistical advantages as well. It does not require a launch pad and while rockets are usually launched during only optimal weather, a commercial jet can take off even if the weather is not 100%. I've been on a plane taking off in overcast while there's a drizzle. That's not something you'd likely do with a rocket launch. The plane can fly above the weather and also it can fly a considerable distance to transport the rocket to be launched at a location which is optimal to achieve the orbit desired. You could have one take off and fly a thousand miles south to take advantage of the earth's rotation and then launch the rocket.

It also does give you something of a velocity boost - not much though. In the case of Pegasus, the L-1011 it is launched from gives it a starting velocity of about 4% of orbital velocity. That's not a whole lot, but it's something, and with a rocket launch, 4% savings isn't something to dismiss.

There have been proposals to use a high flying supersonic aircraft to launch a space vehicle. In that case you could get more than 10% of velocity alone, but it hasn't really developed very far. There are not that many aircraft with the performance and payload for that. Ideas were floated of using the B-58 Hustler in the 1960's. It could fly faster than mach 2. There4 was a project to use it with an air-launched ballistic missile, but that never went anywhere. More recently, the Russian Tu-160 has been suggested as an air launch vehicle.

At this time, I'm only aware of Pegasus as an air launched system.

cjameshuff
2009-Aug-27, 09:16 PM
It might be better to consider launching from an airplane. That is how Orbital Systems Pegasus is launched. There are some logistical advantages as well. It does not require a launch pad

Notice that despite those logistical advantages, Pegasus is the most expensive way per kg to get into orbit. It's also one of the most limited in payload, so if you have a tiny payload and don't want to share a launch, it can be cheaper...but the air launch does not seem to be an advantage in terms of cost.

You also have the logistical disadvantages of arranging to launch from an aircraft in flight. You don't need a pad, you do need a large, highly customized plane, and you still need the big rocket, only you have to attach it to a plane so you can drop and ignite it in mid air. I've never been sure why people think it's vastly easier or cheaper to do things this way rather than launching from a well-equipped facility on the ground.



and while rockets are usually launched during only optimal weather, a commercial jet can take off even if the weather is not 100%. I've been on a plane taking off in overcast while there's a drizzle. That's not something you'd likely do with a rocket launch.

Rockets are often launched in sub-optimal weather. Yes, you do often hear about delays, some rockets are more sensitive than others. And aircraft are not immune, especially when taking off while heavily burdened. I doubt anyone will think it's a good idea to take off in poor weather while loaded with a fully fueled orbital rocket.



The plane can fly above the weather and also it can fly a considerable distance to transport the rocket to be launched at a location which is optimal to achieve the orbit desired. You could have one take off and fly a thousand miles south to take advantage of the earth's rotation and then launch the rocket.

Or you could build a marginally larger rocket. Or launch at sea, without the complications of an air-dropped launch.

Nowhere Man
2009-Aug-27, 10:12 PM
Balloon-lofted rockets (http://en.wikipedia.org/wiki/Rockoon) have been around for a while.

Fred

cjameshuff
2009-Aug-27, 10:54 PM
Balloon-lofted rockets (http://en.wikipedia.org/wiki/Rockoon) have been around for a while.

I remember reading about how Van Allen had problems with the mechanisms for triggering the rocket icing up from the high altitude cold, and solved them with a blanket and cans of heated orange juice.

These were sounding rockets, though. They were getting instruments to high altitude, and then falling essentially straight back down. The altitude the balloon lifted them to basically added directly to the altitude the instruments reached, and was a large fraction of the final altitude achieved. Starting from high altitude is only a very minor benefit to reaching orbit, so you need essentially the same size of rocket as you do for a launch from the ground, but you need to get it to high altitude and launch it in mid air...

Drbuzz0
2009-Aug-28, 05:02 AM
Notice that despite those logistical advantages, Pegasus is the most expensive way per kg to get into orbit. It's also one of the most limited in payload, so if you have a tiny payload and don't want to share a launch, it can be cheaper...but the air launch does not seem to be an advantage in terms of cost.



Pegasus is one of the cheapest (if not the cheapest) dedicated orbital launch vehicles in existence. It has a flyaway cost of about 14 million dollars. The whole thing can send a payload into orbit for about 20 million, services and everything included. (it usually costs a bit more for various reasons).

It's not a big rocket with a huge payload. It never was meant to be. It's a small rocket with a capacity up to 500 kg. For some payloads like demonstrator satellites, small to medium research payloads and some LEO communications relay satellites, that's the cheapest way to launch them.

If you can tolerate the satellite being in an orbit that you don't get to decide on, then you can do it cheaper as a secondary payload, but then you have to go where the primary is headed or at least close to it. If you need to send a small payload somewhere then Pegasus is unbeatable.






You also have the logistical disadvantages of arranging to launch from an aircraft in flight. You don't need a pad, you do need a large, highly customized plane, and you still need the big rocket, only you have to attach it to a plane so you can drop and ignite it in mid air. I've never been sure why people think it's vastly easier or cheaper to do things this way rather than launching from a well-equipped facility on the ground.


That can be a disadvantage or an advantage, depending on the situation. No, you can't launch a huge payload from the air, because the L-1011 wouldn't be able to haul a huge rocket to altitude and even a bigger aircraft, there's going to be a limit.

As far as a well-equipped ground facility: again, that depends. Sea Launch has been successful but it's a big converted platform out in the middle of the ocean. It has to be serviced by helicopter and the rockets are taken on barges. For big rockets, that might turn out to be worth it, but aircraft method turns out to be a much simpler means to the end with a reasonably small rocket.

Jens
2009-Aug-28, 06:26 AM
I've heard of an idea to achieve orbit by using balloons and a craft powered by an ion thruster. Basically, the balloon would provide the lift while the ion thruster slowly created the orbital velocity.

Antice
2009-Aug-28, 09:34 AM
I've heard of an idea to achieve orbit by using balloons and a craft powered by an ion thruster. Basically, the balloon would provide the lift while the ion thruster slowly created the orbital velocity.

That would take some time... err. lots of time. not to mention that i think the air resistance even at max balloon height might overcome whatever thrust you can get with an ion drive.

mugaliens
2009-Aug-29, 07:51 AM
I personally think that the payload of a balloon is pretty low, so it'd be hard to do...

But if the balloons were reusable (as they would be, with proper design), so what?

This is definately thinking outside the box - good idea! It merits further attention.

cjameshuff
2009-Aug-29, 09:39 PM
But if the balloons were reusable (as they would be, with proper design), so what?

So what if the balloons are reusable, if they make only a very minor difference in the size of the rocket required, while limiting you to a miniscule payload and adding to your operating costs? Aside from just the cost of launching a huge balloon, there's also considerations like what to do if something goes wrong with the rocket to prevent a launch....you now have an unguided balloon with a fully fueled, very expensive rocket and payload swinging underneath it that you need to bring down safely.

The energy benefit from a high altitude launch is minimal, about 1.5% if you ignore drag. The biggest difference from a ground launch is that it avoids high speed flight at low altitudes, something does not appear to be a major contributor to launch costs, and it involves lighting the rocket up while it's hanging beneath a floating balloon, something that seems likely to increase costs. You can perhaps use a somewhat lighter aeroshell...you seem better off just building a slightly bigger rocket.

As for JP Aerospace's orbital airship...that proposal involves accelerating an enormous lift envelope with multiple square km of cross section through the upper atmosphere at hypersonic and orbital velocities with ion drives powered by fuel cells. If they're not ignoring basic physics or being very deceptive with what they mean by "orbit", they've left some very major details out. I'm inclined to treat it as seriously as I do Steorn's free energy device...maybe a poorly thought out publicity stunt.

mugaliens
2009-Aug-30, 06:55 AM
Pegasus is one of the cheapest (if not the cheapest) dedicated orbital launch vehicles in existence. It has a flyaway cost of about 14 million dollars. The whole thing can send a payload into orbit for about 20 million, services and everything included. (it usually costs a bit more for various reasons).

While the total mission cost is indeed one of the cheapest, the per kg to LOE cost is among the most expensive.

With a payload of 443 kg, that's $45,000/kg, which is more expensive than the Space Shuttle's $34,000/kg price tag. By comparison, Delta IV's cost about $155 million per launch but can haul upward of 25,000 kg, so the cost is only $6,200/kg, one of the cheapest.

Thus, for small payloads, it can be a "bargain," but piggybacking on other launched missions would be far cheaper.

ugordan
2009-Aug-30, 12:34 PM
Pegasus is one of the cheapest (if not the cheapest) dedicated orbital launch vehicles in existence.
Falcon 1 is currently the cheapest such vehicle AFAIK. As others have pointed out, even if these are the cheapest out there, their cost/kg is among the highest. That's the inherent burden of a small launch vehicle - not all mass and performance parameters in a rocket scale easily. A small vehicle still needs avionics as much as a bigger vehicle (it doesn't get to have miniature avionics, etc.) and will suffer more due to aerodynamic drag losses. It needs a fairing that can be up to several times the vehicle's LEO payload mass. For large vehicles, it's the other way around.

Back on topic, there's no practical benefit to a balloon launched rocket for anything but the smallest of payloads. Only the smallest rockets would benefit from a high altitude launch, and it's not because of being "closer to orbit". Small vehicles (think sounding rockets) typically have really high accelerations and so accumulate high losses in lower atmosphere, again due to drag. By launching from say 20-30 km a good deal of those losses would be alleviated.

For big LVs this is not much of a problem as they have much more mass per vehicle aerodynamic surface area - they feel that drag much less.

ugordan
2009-Aug-30, 12:37 PM
By comparison, Delta IV's cost about $155 million per launch but can haul upward of 25,000 kg, so the cost is only $6,200/kg, one of the cheapest.
Delta IV is far from $155 million, it's probably closer to $200 million and it certainly does not carry 25 tons to LEO.
Delta IV Heavy which can get that big a payload to LEO is more likely to be in the $400+ million range. Consequence of a hydrogen first stage and very low flight rate. Still, I think it might be the most cost-effective of all Delta IVs, though it's nothing to write home about.

Atlas V is much cheaper than Delta IV and more cost effective - NASA flies all its new missions on it and not a single one on a Delta IV. The GOES satellites flown on Delta IV were managed and procured by NOAA, something to do with the satellites being Boeing-built so the vehicle (then Boeing operated) was selected to be the in-house one.

Larry Jacks
2009-Aug-30, 02:27 PM
As cjameshuff correctly pointed out, the advantages of launching a rocket intended for orbit are minimal. Adding to that, the costs of a balloon big enough to carry even the smallest rocket capable of putting a tiny payload into orbit would be substancial. Add to that the operational challenges of launching such a large balloon. Even with decades of experience, launching a large research balloon is a challengine exercise. A balloon capable of carrying even a minimal orbital rocket would be many times larger than the largest balloon currently used.

Add to that the expense of the balloon and the lifting agent. If you use hydrogen, the lifting capacity is higher and the costs are lower than helium. Helium isn't cheap even from the Strategic Helium Reserve.

eburacum45
2009-Aug-30, 03:27 PM
There is a balloon-supported concept that might be useful; the suspended-track Space Launch System. From here
http://www.winwenger.com/launch.htm

...a very long track—a reusable track system stably supported overtop most of the Earth's atmosphere for hundreds of miles, long enough to give very gentle launches and still build the requisite speeds;
Supported by hydrogen (preferred) or helium (if required) or heated-air (if the engineering and power supply and/or insulation parameters can be so configured) balloons or air-buoyant enclosures;
Tethered in triangular or geodesic-configured networks, to each other and to the ground, maintained in alignment by laser-guided computers and cable-tighteners.
Payloads would be launched up the track, energy supplied through the track continuously for hundreds of miles, to accumulate the necessary orbital (or sub-orbital, ballistic in the case of intercontinental transports) speed from a very gentle acceleration. No reaction-mass, boosters (except maybe a small JATO-type unit applied at the end to change trajectories), tanks or other expensive hardware would be sacrificed after one use. Instead, the atmosphere, serving as structural ally, becomes the means for transfer of moment of impulse. The balloon-supported track would deform with each launch, then re-configure and re-form within the hour to support the next launch.

mugaliens
2009-Aug-31, 07:22 AM
That's the inherent burden of a small launch vehicle - not all mass and performance parameters in a rocket scale easily.

Exactly, which is why we use supertankers for transporting oil as opposed to a hundred smaller ones.


A small vehicle still needs avionics as much as a bigger vehicle (it doesn't get to have miniature avionics, etc.) and will suffer more due to aerodynamic drag losses. It needs a fairing that can be up to several times the vehicle's LEO payload mass. For large vehicles, it's the other way around.

The other scaling factor is one of weight (propellant) fraction. This is largely overcome by increasing the acceleration. For example, we now fire complex electronics and the weapons payload they're guiding out of the barrels of 155 mm howitzers (M712 Copperhead (http://en.wikipedia.org/wiki/M712_Copperhead)), as it's cheaper and more reliable than putting the same payload on a rocket. It's possible for us to scale this to super-cannon status, firing some non-living payload into space. Some propellants are all but totally shockproof but would work ok at apogee for an insertion burn.

But the electronics would have to be very, very tiny, and very durable.


Back on topic, there's no practical benefit to a balloon launched rocket for anything but the smallest of payloads. Only the smallest rockets would benefit from a high altitude launch, and it's not because of being "closer to orbit". Small vehicles (think sounding rockets) typically have really high accelerations and so accumulate high losses in lower atmosphere, again due to drag. By launching from say 20-30 km a good deal of those losses would be alleviated.

For big LVs this is not much of a problem as they have much more mass per vehicle aerodynamic surface area - they feel that drag much less.

I think you nailed it, ugordon.

Drbuzz0
2009-Sep-02, 03:36 PM
While the total mission cost is indeed one of the cheapest, the per kg to LOE cost is among the most expensive.

With a payload of 443 kg, that's $45,000/kg, which is more expensive than the Space Shuttle's $34,000/kg price tag. By comparison, Delta IV's cost about $155 million per launch but can haul upward of 25,000 kg, so the cost is only $6,200/kg, one of the cheapest.

Again: that all depends. If you have a payload and it is going to be in a fairly standard orbit that you can get it to as a secondary payload then that's fine. If you have a satellite that needs to be in some very specific orbit that is not the same as many others then Pegasus is your cheapest option.

Lets say you have a satellite that is doing auroral research and you want it to observe both the northern and southern auroras from varying altitudes, ideally more than once a day. You would need it to have a short-duration polar orbit that is highly elliptical.

Good luck finding a primary payload with the proper launch perimeters necessary to get you anywhere near that kind of orbital objective.

Thus, Pegasus is the cheapest dedicated launcher and in some circumstances, you need a dedicated launcher.

It's like trying to bum a ride to an unpopular destination. You have a problem because nobody is going your way.





Thus, for small payloads, it can be a "bargain," but piggybacking on other launched missions would be far cheaper.

Air launching is helpful for small payloads because something like Pegasus is not difficult to haul to a reasonable altitude with something like an L-1011. It also is a high acceleration rocket that benefits from less air resistance.

To get any real savings with a big payload launcher you're going to need to haul it to as high an altitude and speed as possible. If you can get it up to 60,000 feet and mach 2+ then you might have enough to justify air launching. If you have enough altitude and can get a good ~10% of orbital velocity then you'll get some noticable savings.

Of course, the problem is that there are not very many aircraft capable of carrying a big rocket up to that kind of altitude and speed. One that I can think of is the Russian Tu-160 - it has the payload and speed, but it's not designed for big external payloads like that. So it would need to be modified quite a bit.

So it's not really worth it with what we have. What would be needed is something like an XB-70 on steroids and designed expressly for space launches.

joema
2009-Sep-04, 03:34 AM
...If you can get it up to 60,000 feet and mach 2+ then you might have enough to justify air launching. If you have enough altitude and can get a good ~10% of orbital velocity then you'll get some noticable savings...What would be needed is something like an XB-70 on steroids and designed expressly for space launches.
Even 60,000 ft and Mach 2 isn't much help. It might be 10% orbital velocity, but only about 1% of the required kinetic energy.

The key to understanding this is the kinetic energy equation KE = 1/2mv^2, where
KE = kinetic energy (joules)
m = mass in kg
v = velocity in m/s.

The v^2 term is what relegates air launch (balloon or otherwise) to fringe applications. E.g, for a fixed 1,000 kg payload mass, Mach 2 is about 10% of orbital velocity but only about 1% of orbital kinetic energy. That means you only saved 1%, yet it cost you a vehicle capable of lifting the booster to 60,000 ft and Mach 2.

This also illustrates why a Mach 3 XB-70 also won't help. It's even more expensive, more complex, and doesn't help much more. IOW as Mach increases, the expense and technical risk of the airbreathing launch platform rises faster than the benefit accrued.

Larry Jacks
2009-Sep-04, 01:13 PM
This also illustrates why a Mach 3 XB-70 also won't help. It's even more expensive, more complex, and doesn't help much more. IOW as Mach increases, the expense and technical risk of the airbreathing launch platform rises faster than the benefit accrued.

Good points, and air launch at Mach 3 has proven to be a challenging and risky engineering proposition. Back in the 1960s, Lockheed developed 2 versions of the A-12 Oxcart (http://en.wikipedia.org/wiki/Lockheed_A-12) that faced this problem. They were the YF-12A (http://en.wikipedia.org/wiki/Lockheed_YF-12) interceptor (3 were built) and two [http://en.wikipedia.org/wiki/Lockheed_D-21/M-21"]M-21[/URL] drone carriers (the drone was the D-21). They eventually overcame the challenges of firing an air-to-air missile from the YF-12A but it wasn't easy. IIRC, they didn't just drop the missiles from the weapons bay, they threw them out with a fair amount of downward force.

The M-21 carried the D-21 on top of the fuselage. During one test launch, the D-21 apparently flamed out just after separation and collided with the M-21. The M-21 was destroyed and the back seater was killed. The surviving M-21 is in Seattle's excellent Museum of Flight.

Drbuzz0
2009-Sep-06, 09:40 PM
Even 60,000 ft and Mach 2 isn't much help. It might be 10% orbital velocity, but only about 1% of the required kinetic energy.

The key to understanding this is the kinetic energy equation KE = 1/2mv^2, where
KE = kinetic energy (joules)
m = mass in kg
v = velocity in m/s.

The v^2 term is what relegates air launch (balloon or otherwise) to fringe applications. E.g, for a fixed 1,000 kg payload mass, Mach 2 is about 10% of orbital velocity but only about 1% of orbital kinetic energy. That means you only saved 1%, yet it cost you a vehicle capable of lifting the booster to 60,000 ft and Mach 2.

This also illustrates why a Mach 3 XB-70 also won't help. It's even more expensive, more complex, and doesn't help much more. IOW as Mach increases, the expense and technical risk of the airbreathing launch platform rises faster than the benefit accrued.

First, you're ignoring the other advantages, including the fact that many rocket engines have a total reduction in effeciency at sea level of up to 30% and that more than 90% of the energy lost to drag occurs during the very first phase of the rocket launch.

By the way: I never said that launching something at mach 3 at 60,000 feet would be easy. It's obviously not, and considering that we don't have such a suitable aircraft, it would have to be developed. It probably is not worth while at this point. I'm talking theoretically - if you had the ability to carry something up that high and fast.

If that were the case, it would be better to drop the spacecraft and have it light up after falling a short distance. Much safer that way. That approach has proven to be highly successful and safe for air launching various rockets, missiles and such things. Mounting it on top, like the Lockheed D-21 turns out to be a lot more problematic.

ugordan
2009-Sep-06, 10:04 PM
other advantages, including the fact that many rocket engines have a total reduction in effeciency at sea level of up to 30%
If you're talking about Isp, that's more like 10%.

mugaliens
2009-Sep-07, 01:34 AM
There's another D-21 at the Evergreen Aviation Museum....

Larry Jacks
2009-Sep-07, 01:40 AM
Yes, they have an SR-71 and a D-21 at the Evergreen Museum in McMinneville, OR, as well as the Hughes Hercules (AKA "Spruce Goose") and many other good planes. Many of their planes are reportedly still airworthy. It's a good museum.

The Seattle Museum of Flight has the only remaining M-21 with a D-21 mounted on top. The D-21 is a wicked fast looking aircraft (reportedly Mach 4) powered by a ramjet engine. Ultimately, it wasn't really a successful program probably because it was just too far ahead of its time. After the accident that destroyed an M-21 and killed the backseater, they tried launching D-21s from B-52s with rocket assist. The operational history wasn't good and it was very expensive.

mugaliens
2009-Sep-08, 07:27 AM
The Seattle Museum of Flight has the only remaining M-21 with a D-21 mounted on top.

Ah.

Your comments on the D-21 are right on the money, Larry!

- Mugs

publiusr
2009-Sep-14, 07:20 PM
Stabilo combined balloon launch with a tractor rocket which was also an escape tower.

Here is a small LV that might be perfect for balloon launch--if it works
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V1N-4T4WKVP-1&_user=10&_coverDate=01%2F31%2F2009&_rdoc=7&_fmt=high&_orig=browse&_srch=doc-info(%23toc%235679%232009%23999359998%23712060%23F LA%23display%23Volume)&_cdi=5679&_sort=d&_docanchor=&_ct=17&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=cb7f907a88d27ccabc90741dc27519de

Ara Pacis
2009-Sep-15, 07:09 AM
I've posted my own baloon-assisted launch idea around here a couple of times.

It's a little different. Instea of a balloon, it's a rigid-airship/dirigible/zeppelin that is very large, long, with a very narrow aerodynamic shape (think Sears-Haack body) with wings for increased lift and perhaps optimized for a hypersonic compression lift at a high speed flight regime. It would not carry a large payload, but perhaps an extremely lightweight passenger craft.

I'm not even sure it's doable, but if there's a way to use lighter-than-air tech to aid with rocketry, it's probably going to have to be fast as well, and not a randomly floating balloon.

sanman
2009-Sep-15, 12:38 PM
I think that if you want to launch from that high - away from the comforts of a ground station - then it should be for a reason. For instance, if your rocket engine is starting at an altitude where the air is very thin and perhaps slightly more ionized, then maybe it's possible to use some kind of electric/magnetic thruster instead of a combustion engine. The caveat would be that such an engine would have to be of comparably high thrust, which perhaps only a couple of technologies like MHD or PIT could do, and even then they would require a nuclear reactor.

I'm thinking that a balloon could be used for something cooler, like stationing personnel and equipment at the upper edge of the atmosphere for prolonged periods of time, so that we could test out systems required for long duration space missions. Perhaps it would be possible to test a plasma bubble protection system as an active radiation shield by floating it high on a balloon, without having to go into space. Perhaps it would be possible to float a Poor Man's Hubble telescope near the top of the atmosphere, to take beautiful Hubble-style photos at a lower cost without launching it into space on a rocket.