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jrkeller
2009-Sep-15, 01:58 PM
On September 12th 2009, Armadillo Aerospace flew a test vehicle that simulates the next version of a Lunar Module. It is part of the XPrize competitions. The vehicle was required to ascend to a height of 50 meters, translate horizontally to a landing pad 50 meters away, land safely on a rocky lunar-replica surface after at least 180 seconds of flight time, and then to repeat the flight by returning to the original launch site. It did it twice.

A more detailed article, with videos can be found here (http://www.spaceref.com/news/viewpr.html?pid=29158).

Was is interesting from an Apollo hoax debunking POV is that this vehicle, which generates about 2000 lbs of thrust hovers over the landing site both during landing and liftoff for many seconds and doesn't create a blast crater. There's even a camera view from the vehicle which shows the exhaust hitting the surface and no crater was formed. We now have some very clear evidence that rocket engines do not create blast craters.

Swift
2009-Sep-15, 03:18 PM
We now have some very clear evidence that rocket engines do not create blast craters.
Oh, that just what THEY (TM) want you to think. It really proves that Armadillo Aerospace hoaxed the test. :D

slang
2009-Sep-15, 03:41 PM
Oh, that just what THEY (TM) want you to think. It really proves that Armadillo Aerospace hoaxed the test. :D

Hehe... after all, John Carmack is an expert in 3D simulations :)

Seriously, a great achievement. Wonderful to see that beasty fly.

Torsten
2009-Sep-15, 04:27 PM
Also, didn't the nozzle on the Apollo LM have a much larger diameter, such that the pressure per unit area was quite low? This machine appears to have a very small nozzle, and with ~2000 pounds of thrust, the psi is probably higher than for the Apollo LM. It would be interesting to compare the actual numbers - but that might really confuse a hoax believer.

NGCHunter
2009-Sep-15, 06:15 PM
Oh, that just what THEY (TM) want you to think. It really proves that Armadillo Aerospace hoaxed the test. :D

You're being sarcastic, but there was a time when I spent a few weeks going back and forth with a hoax believer who seriously argued that Armadillo Aerospace fakes all their videos (because it's impossible to vertically land a rocket, but jets are somehow ok :doh:). His main point of "evidence" was the former occupation of John Carmack, as well as Nvidia's sponsorship. Some people are truly beyond all help. Anyway, I'm glad to hear Armadillo finally met their goal.

slang
2009-Sep-15, 06:34 PM
All I can say is this looks nothing like a Quake rocketjump :)

Fazor
2009-Sep-15, 06:38 PM
All I can say is this looks nothing like a Quake rocketjump :)

Different class. The PRJ (Personal Rocket Jump) is a defensive maneuver employed in and around space stations. They're developing that technology too, for the Martian extermination campaign. They just don't release those videos to the public.

Count Zero
2009-Sep-15, 07:53 PM
What threw me was aat the end of the first video, when a man ran up to the vehicle with a fire extinguisher. Without any recognizable visual references, I had completely misjudged the size of the craft. It looked like little more than a toy, but it's at least 12-feet tall - roughly 2/3rds the size of the Soviet LK lunar module (http://www.myspacemuseum.com/eurolk.htm).

Skyfire
2009-Sep-15, 09:02 PM
What threw me was aat the end of the first video, when a man ran up to the vehicle with a fire extinguisher. Without any recognizable visual references, I had completely misjudged the size of the craft. It looked like little more than a toy, but it's at least 12-feet tall - roughly 2/3rds the size of the Soviet LK lunar module (http://www.myspacemuseum.com/eurolk.htm).

You know, that Soviet lunar module does look - in their 'heavy engineering and lots of plumbing' kind of way - functional. I always felt it was a bit of a shame they couldn't get their main lifter rocket off the ground without destroying the launch pad in the explosion!

Obviously much speculation has gone on about whether they had all the equipment ready for use if they could just figure out how to lift the whole lot off the ground.

crookster_man
2009-Sep-15, 09:56 PM
Well I think you need to answer a few questions before you and safely assume your hypothesis is correct.

1. What was the replica made out of? Lunar material or just look alike?
2. What impact does Earth's gravity have on the equation versus the Moons?
3. What impact would a vacuum have on the test?

As for not creating a blast crater I did notice at the end of the first video the landing material began to give way...

I actually believe the moon landings did happen btw, but you shouldn't jump to conclusions.

JonClarke
2009-Sep-15, 10:54 PM
I spent a few weeks going back and forth with a hoax believer who seriously argued that Armadillo Aerospace fakes all their videos (because it's impossible to vertically land a rocket, but jets are somehow ok :doh:).

Did you thow Nulka at them?

http://en.wikipedia.org/wiki/Nulka

http://www.youtube.com/watch?v=8AFGtIkSf30&feature=related

R.A.F.
2009-Sep-15, 10:56 PM
One of the very first things Armstrong mentions when he sets foot on the Moon is that there was no discernable crater left by the descent engine. If NASA were attempting to "hide" this fact, then it seems rather idiotic that Armstrong would he say it for all the world to hear.

jrkeller
2009-Sep-15, 11:48 PM
One of the very first things Armstrong mentions when he sets foot on the Moon is that there was no discernable crater left by the descent engine. If NASA were attempting to "hide" this fact, then it seems rather idiotic that Armstrong would he say it for all the world to hear.


But he was trying to give a hint to the world that is was fake. According to those lunar experts Percy and Bennett.

BigDon
2009-Sep-16, 01:11 AM
A small aside if I may.

Is the magenta color of the exhaust plume a direct result of the ethenol/LOX fuel burning or is the plume reacting with the atmosphere to produce the color?

R.A.F.
2009-Sep-16, 01:52 AM
But he was trying to give a hint to the world that is was fake. According to those lunar experts Percy and Bennett.

Is that Lunar or Looney?? :)

Dave J
2009-Sep-16, 02:39 AM
Well I think you need to answer a few questions before you and safely assume your hypothesis is correct.

1. What was the replica made out of? Lunar material or just look alike?
2. What impact does Earth's gravity have on the equation versus the Moons?
3. What impact would a vacuum have on the test?

As for not creating a blast crater I did notice at the end of the first video the landing material began to give way...

I actually believe the moon landings did happen btw, but you shouldn't jump to conclusions.

If the landing surface was supposed to be a lunar "replica", it didn't seem very convincing. I didn't see any dust, just pretend- looking rock thingys. I doubt that was intended to be a real part of this test flight.

The gravity, be it Earth or Moon, is just what needs to be overcome (by engine thrust) for a controlled hover, descent and landing. This test required a 2000 pound engine to overcome the 1g weight of the test article. In lunar gravity, it would only have required around 330lbf to hover.

Vaccuum flight would require a different nozzle configuration to (attempt to) overcome the overexpansion phenomenon in thin atmospheric/vaccuum environments. This overexpansion greatly increases the area of the plume impingement on the surface, and reduces the surface impact by area. You wouldn't see a nice pencil-sharp exhause plume like that in a vaccuum, that nozzle was specifically designed for near surface atmospheric pressure operation and efficiency.

That's my layman's explanation.

oh and the red exhaust...obviously an Aerotech Redline (TM) motor ;)

nomuse
2009-Sep-16, 10:07 AM
Well I think you need to answer a few questions before you and safely assume your hypothesis is correct.

1. What was the replica made out of? Lunar material or just look alike?
2. What impact does Earth's gravity have on the equation versus the Moons?
3. What impact would a vacuum have on the test?

As for not creating a blast crater I did notice at the end of the first video the landing material began to give way...

I actually believe the moon landings did happen btw, but you shouldn't jump to conclusions.

And you could read some old posts on this board, where these questions have been discussed in detail.

The X-prize landing surface is not designed to behave materially like the lunar surface; it is mostly intended to have the same sloping, boulder-strewn shape: http://thelaunchpad.xprize.org/2009/09/ngllc-09-lunar-landing-pad.html

Earth's gravity means 6x the necessary thrust just to leave the ground.

Vacuum also favors the Moon; air constrains the exhaust, forcing it into a narrower shape. It also provides much more bulk to shift and entrain particulates.

In essentials, if you did have a duplicate lunar surface here on Earth, it would be rather more torn up by a representative landing.

Jason Thompson
2009-Sep-16, 11:41 AM
As for not creating a blast crater I did notice at the end of the first video the landing material began to give way...

Yes it did, but only after a long period of hovering. Here are the factors that make this a good indicator of whether a LM should blast a crater out of the ground:

1: This thing had a much smaller engine nozzle. The LM descent stage was generating about 3,600lb of force when it touched down, and its engine nozzle was 54 inches across. Do the calculations and that means that the pressure at the engine nozzle exit was about 1.6psi. Just eyeballing that video, it looks like the engine nozzle of that vehicle was at most 12 inches across. If it was generating 2000lb of thrust (as a minimum, since the artcle stated it weighed 1900lb fully fuelled, so much have generated in the region of 2000lb to get off the ground in the first place) then the pressure at the nozzle exit is about 17.7psi, much more than the LM was generating.

2: This vehicle was tested in an atmosphere, which has the effect of confining the exhaust plume. In other words the pressure exerted by the exhaist doesn't drop as rapidly as you move away from the nozzle exit as it would in the vacuum on the Moon. So, considerably more pressure applied in a more confined plume, therefore considerably more force applied to the surface this thing is landing on compared to the LM acting on the lunar surface.

3: It hovered over the same spot at the same altitude for a long time, which the LM never did.

4: The 'giving way' of the surface you see is almost certainly spalling. The surface appears to be a concrete platform. If you heat up concrete or other similar materials, for example by aiming a hot rocket plume at them for several seconds) the thermal stresses and distortion eventually lead to sudden failure and fragments coming off.

That rocket was not digging a crater, not by any means, and since, as I have just shown, the effect of the LM descent engine on the surface of the Moon was considerably milder than the effect of this rocket on the ground, there is no reason that the LM should have dug a crater either.

NGCHunter
2009-Sep-17, 02:00 PM
Did you thow Nulka at them?

Nope, never knew about that one before. Very interesting, I'll file that one away for later use, thanks.

JayUtah
2009-Sep-17, 02:21 PM
...

1. What was the replica made out of? Lunar material or just look alike?

Neither; it looks pretty much like concrete to me. As such it would be considerably more resistant to erosion than either Earth or lunar soil. Clearly it would be unwise to claim that the surface in this test is identical in hardness to the lunar surface.

2. What impact does Earth's gravity have on the equation versus the Moons?

It requires more thrust from the rocket to maintain flight. That is, for a spacecraft of a given mass, it will require six times more thrust to hover that spacecraft over Earth's surface than over the Moon's surface. That means a more powerful rocket plume.

3. What impact would a vacuum have on the test?

Considerable. In air, an exhaust plume is constrained to a column, assuming the nozzle has been properly designed. This is what you see in the video. In a vacuum the plume begins to expand immediately upon exiting the nozzle. This is because the plume retains some static pressure. It is not possible to design a convergent-divergent nozzle that can expand the plume optimally in a vacuum. The rule of thumb is that 90 percent of the exhaust plume mass will be contained in a cone with a 45-degree half-angle extending downward from the nozzle exit plane.

Further, that static pressure accounts for up to 40 percent of the overall thrust in a vacuum. So if you require 10,000 N of thrust to hover a certain spacecraft in a certain gravity field, up to 4,000 N of it will be simply from the static pressure at the exit plane. This leaves only 6,000 N to be produced by momentum thrust. And only momentum thrust applies to the strength of the plume as it impinges on an underlying surface.

We are accustomed informally to divide the thrust by the area of the nozzle exit plane in order to derive the distributed gas load. This is actually the most severe case. Applying the cone approximation above to the momentum-only component of thrust, and accounting for altitude, more closely approximates the dynamic fluid load on an underlying surface.

As for not creating a blast crater I did notice at the end of the first video the landing material began to give way...

Thermal spalling. The particular way in which it erodes is characteristic of portions of concrete "popping" under the heat load. It is a function of the heat of the plume, not its gas pressure. I can hold an acetylene torch over a concrete surface and cause the exact same behavior, even though the torch exerts negligible gas pressure on it.

Torch2k
2009-Sep-18, 05:04 PM
A more detailed article, with videos can be found here (http://www.spaceref.com/news/viewpr.html?pid=29158).

A very interesting video, but it shows something that has me wondering.

I notice that the exhaust plume exhibits evenly-spaced bright 'bands', and that their spacing changes depending on thrust. I can't recall whether I'd seen this before, but then again, most rockets aren't stationary, and not all propellants produce such a beautiful translucent plume.

I have since found other videos (mostly of static tests) showing these bands. I presume they're related to pressure, engine harmonics, and possibly the frame rate of the video equipment? Or is it a combination of all three? Or am I totally out to lunch?

Would appreciate if one of our resident 'rocket scientists' could briefly explain them.

Donnie B.
2009-Sep-18, 05:06 PM
I believe that what you're seeing is the phenomenon of "shock diamonds", which is well known in turbojet as well as rocket exhaust plumes.

http://en.wikipedia.org/wiki/Shock_diamond
http://www.aerospaceweb.org/question/propulsion/q0224.shtml

Torch2k
2009-Sep-18, 05:23 PM
That would be them, and in fact I can now recall seeing them before in photos of the SR-71 (for example). Would never have come up with 'shock diamonds' or 'mach disks' to use as search terms, so thanks very much for supplying that term.

Supersonic fluid dynamics, huh? Sounds like something potentially harmful to the brains of mere mortals like myself.

BigDon
2009-Sep-18, 07:35 PM
That would be them, and in fact I can now recall seeing them before in photos of the SR-71 (for example). Would never have come up with 'shock diamonds' or 'mach disks' to use as search terms, so thanks very much for supplying that term.

Supersonic fluid dynamics, huh? Sounds like something potentially harmful to the brains of mere mortals like myself.

Tomcats in zone 5 afterburner produce those as well. Though those big honking SAMS we had moved so fast it looked like a bad cartoon and you couldn't see anything but the white exhaust plume going up to the stratosphere.

Talos missiles! That's it. Things were bigger than telephone poles. Almost 40 feet long and weighed over 5 tons with the first stage attached yet moved so fast that unless you were already looking at where it was going you couldn't track it by eye.

If you were watching the launcher when it fired by the time you glanced up at it it would be tiny and receding and the only way you could still follow it is the dense white exhaust plume.

Hobbitmode: "Didn't seem quite natural I tell ya!" :EndHobbitmode

We shot a bunch off because they were retiring them.

NickW
2009-Sep-19, 12:49 AM
Shock diamonds? I always wondered why that happened but never thought to ask the question. Gotta love spending time on BAUT. Learn something new everyday.


Actually, I learn to much in a day here :)

Dave J
2009-Sep-19, 02:56 PM
In the shuttle post launch analysis of footage, the team looks at the formation of the diamonds directly behind the SSMEs as the engines come up to full power. They time the formation to tiny fractions of a second to analyze engine performance in the first few seconds of engine start.
Fascinating stuff.

Ong
2009-Sep-19, 03:20 PM
Cool video! How do they keep that rocket stable, vertical? I don't see any relevance to the original post, though. The landing surface appears to be concrete, not very fine powdery sand.

captain swoop
2009-Sep-19, 07:23 PM
Talos missiles! That's it. Things were bigger than telephone poles. Almost 40 feet long and weighed over 5 tons with the first stage attached yet moved so fast that unless you were already looking at where it was going you couldn't track it by eye.

If you were watching the launcher when it fired by the time you glanced up at it it would be tiny and receding and the only way you could still follow it is the dense white exhaust plume.

Sounds like the old 'Seaslug' long range missiles the County Class destroyers carried. They had solid rocket boosters to get them up to speed so the jet could take over (maritime version of the RAF Bloodhounds)
They went up at a fantastic speed and left a huge smoke trail from the solid fuel boosters.

But I am getting off topic sorry.

BigDon
2009-Sep-21, 03:59 AM
Captain, one time we fired one of those at one of our aircrews. On purpose no less.

A missile shoot that was excruciatingly thought out. Took it head on with a AIM 7M Sparrow. There's more but I don't wish to hijack.

captain swoop
2009-Sep-21, 01:53 PM
quite right. might make a story in Babbling though.

cjl
2009-Sep-22, 07:32 PM
Cool video! How do they keep that rocket stable, vertical? I don't see any relevance to the original post, though. The landing surface appears to be concrete, not very fine powdery sand.
I would guess that the primary method of control is the gimballing of the engine - they actively change the nozzle direction (slightly) to offset any imbalances. In parts of the video, you can see this occurring if you watch carefully.

JayUtah
2009-Sep-22, 11:17 PM
Cool video! How do they keep that rocket stable, vertical?

Closed-loop control and vectored thrust, the same way we've done it for 50 years.

Extravoice
2009-Sep-23, 04:25 PM
Closed-loop control and vectored thrust, the same way we've done it for 50 years.

Okay, this is off topic, but why did the Saturn 5 have fins? Was thrust vectoring inadequate at some point in its flight, or did VonBraun simply like fins? :)

gwiz
2009-Sep-23, 04:33 PM
Okay, this is off topic, but why did the Saturn 5 have fins? Was thrust vectoring inadequate at some point in its flight, or did VonBraun simply like fins? :)
For any rocket, there's a trade-off between the added mass of fins and the saving in fuel budget for attitude control that comes with an aerodynamically stable vehicle.

JayUtah
2009-Sep-23, 04:58 PM
Attitude control by means of thrust vectoring has a negligible fuel penalty on a nominal ascent. The Saturn V had fins because von Braun liked fins.

Dave J
2009-Sep-23, 06:07 PM
The original Saturn 1 had no fins...

Extravoice
2009-Sep-23, 07:41 PM
Attitude control by means of thrust vectoring has a negligible fuel penalty on a nominal ascent. The Saturn V had fins because von Braun liked fins.

That's some serious clout. I can imagine the exchange during the design review:

Engineer: Why the fins?
VonBraun: I like fins.
Engineer: Okay.

JayUtah
2009-Sep-23, 07:56 PM
As I recall there was some handwaving about airflow around the outboard F-1 nacelles, but it didn't really amount to a data-driven engineering justification.

AtomicDog
2009-Sep-23, 08:06 PM
That's some serious clout. I can imagine the exchange during the design review:

Engineer: Why the fins?
VonBraun: I like fins.
Engineer: Okay.

It's a good thing, then, that the enigeneer's previous job wasn't at Cadillac.

Mellow
2009-Sep-24, 05:40 AM
As I recall there was some handwaving about airflow around the outboard F-1 nacelles, but it didn't really amount to a data-driven engineering justification.

Gosh I had never heard that before and I actually find it reassuringly normal that Dr. W V-B
might flex his organisational might in this way. Even in the greatest minds, sometimes the pointy haired boss tries to get out.

JayUtah
2009-Sep-24, 11:44 AM
Hey, I think the Saturn V looks really cool with fins.

Extravoice
2009-Sep-24, 01:17 PM
This is drifting pretty-far off topic (but why not;)).

A quick google search found the following claim, for which I couldn't find any collaborating information (in the minute I devoted to it). "The fins would maintain enough stability to give time for the escape tower rockets to be a activated."

It could just be wishful thinking on the part of the author, though.

Donnie B.
2009-Sep-24, 06:51 PM
One thing's for sure: they only had effect (if any) during the first 150 seconds of the mission. I suppose by the time the S-II kicked in they were above most of the atmosphere.

Good thing Huntsville didn't design the LM, though -- they might have put fins on it too!

captain swoop
2009-Sep-24, 10:21 PM
One thing's for sure: they only had effect (if any) during the first 150 seconds of the mission. I suppose by the time the S-II kicked in they were above most of the atmosphere.

Good thing Huntsville didn't design the LM, though -- they might have put fins on it too!

and Running Boards?

Starfury
2009-Sep-24, 11:29 PM
And cool blue lights and a kickin' sound system. :) :lol:

Donnie B.
2009-Sep-24, 11:46 PM
My dad said, "Son, you're gonna drive me to hummin'
If you don't stop flyin' that hot rod Grumman."