Space X to build reusable launch vehicle

D Tibbets · Post by **D Tibbets** » Sun Oct 02, 2011 9:37 pm

The extra fuel needed to overcome the additional maneuvers and landing would be substantial, but probably much less than 2 X. If atmospheric turbulence can be mastered, the first stage might be the most demanding. If they intend to reverse direction and land at the launch site, the accumulated velocity will need to be reversed (several thousand MPH?),admittedly at much less weight than the pad launch weight. Add to that the landing requirements fuel and structure, and atmospheric maneuvering requirements. Landing the first stage at a down range site would help, but except for Russia, there is only water.

The second stage may be easier, there is less less weight, and reentry does almost all of the deceleration, and presuming it reaches orbital velocity, little fuel would be needed for a de orbit burn and little other thrust would be needed for it to descend to the launch site. It might need to orbit for a week before an optimal orbital trajectory would bring it over the launch site, but the only cost would be time.. Heat shields are well developed. This leaves only parachutes/ drag, and or rockets to manage descent speed,with final deceleration at landing.

Has there ever been a successful reentry of a cylindrical body, as opposed to the typical cones or complex lifting body design of the Shuttle?

Dan Tibbets

Skipjack · Post by **Skipjack** » Mon Oct 03, 2011 1:27 am

I wonder if the secret sauce for first stage RTLS is deployable membrane wings, a la draco lizard:

Like the concept TGV has been sitting on for a decade or two, trying to get the funds to build their RLV.

Ray · Post by **Ray** » Mon Oct 03, 2011 8:08 am

I think it worth pointing out that if all parts of the rocket are re-usable then you can simply use bigger rockets to get a set target mass into orbit. Who cares if you need an extra stage, more engines and three times the fuel to get a payload into space if the only cost you are paying is for the fuel, which is dirt cheap compared to the other parts?

rjaypeters · Post by **rjaypeters** » Mon Oct 03, 2011 11:21 am

D Tibbets wrote:Has there ever been a successful reentry of a cylindrical body, as opposed to the typical cones or complex lifting body design of the Shuttle?Dan Tibbets

The Shuttle Solid Rocket Boosters (SRBs) didn't go through a full re-entry, but encountered much of the same dynamics.

In general, bodies of revolution are statically unstable from an aerodynamic perspective, so SRBs used drogue and parachutes pretty quickly after they detached from the fuel tank, so the SRB was not really going through re-entry as a body.

Several years ago, I read part of an AIAA paper by a student who wanted to spin Shuttle fuel tanks with the long axis perpendicular to the re-entry velocity vector as a method to bring to earth materials gathered from space. The [edit]Magnus[/edit] effect would give the tank lift and the angular momentum would control (it was hoped) the re-entry path. Entry heat would be dissipated by the continuous rotation. Pretty wild, huh?

I can't find the paper with a quick search, but I didn't look very hard.

Anyway, I don't think Mr. Musk is planning to spin his re-entering stages. It looks like the first stage might be using a fully powered entry. Great, if the gas is available.

Skipjack · Post by **Skipjack** » Mon Oct 03, 2011 4:18 pm

I guess that conic shapes are better, even for a nose first reentry in regards to stability (and probably even adding a little cross range). The DC-X was a conic shape and was meant to do that.
I am wondering whether SpaceX will slightly change the shape of the first stage to something more conical, but did not show that in the video.

choff · Post by **choff** » Mon Oct 03, 2011 5:27 pm

Apparently the latest Chinese launch propaganda video was playing 'America the Beautiful' in the background.

http://www.hindustantimes.com/Patriotic ... 52146.aspx

93143 · Post by **93143** » Mon Oct 03, 2011 7:20 pm

ladajo wrote:How do you turn the engines around in a "few days"? The shuttle engine turnarounds were certainly longer than a "few days", and that does not even consider the test burns at Stennis between flights.

Skipjack wrote:By not operating them 10% above design specs?

The SSME Block III was getting close to ready, and it was supposed to go 10 flights without even needing to be removed from the orbiter.

Also, the standard power level for an SSME was 104.5%, not 110%. There's nothing magic about 100%; it's just what they were originally aiming at, and testing showed that they could go higher without overstressing the engine, so they did.

Skipjack · Post by **Skipjack** » Mon Oct 03, 2011 9:21 pm

Oh well, so 105%.
Those 105% though meant hat they had to thoroughly check every engine after every single flight.
It is very expensive and not cost effective. You leave some savety margins and operate below design specs, you can skip the inspection.
As I said, you dont have to inspect the engines of an airliner after every flight either. Not even of a Fighter Jet (though they do need some more inspection as they do operate closer to their limits).

93143 · Post by **93143** » Tue Oct 04, 2011 12:14 am

They'd have had to do much the same thing at 100%. It's effectively an arbitrary reference point; observed real-world behaviour trumps "design specs". Beyond 104.5%, yes, things start to get more risky...

With the Block III, the engine internals would have been monitored closely enough that disassembly and precautionary overhauling wouldn't have been necessary.

How low do you think the performance of an SSME needs to go before it no longer needs either disassembly or advanced health monitoring? 100% won't do it. 95%? 90%? 80%? How much Isp would you lose running at lower pressures like that?

Of course, a Merlin 1 doesn't have the same stringent requirements that drove the RS-25 design. It runs at a much lower pressure, and it uses a gas generator cycle rather than staged combustion. It has a very high T/W, but not stunningly high for RP-1. Assuming they had reuse in mind when they designed it, it's probably much easier to get to the level of reusability represented by the SSME Block III, or perhaps even better.

IntLibber · Post by **IntLibber** » Tue Oct 11, 2011 9:07 am

93143 wrote:They'd have had to do much the same thing at 100%. It's effectively an arbitrary reference point; observed real-world behaviour trumps "design specs". Beyond 104.5%, yes, things start to get more risky...

With the Block III, the engine internals would have been monitored closely enough that disassembly and precautionary overhauling wouldn't have been necessary.

How low do you think the performance of an SSME needs to go before it no longer needs either disassembly or advanced health monitoring? 100% won't do it. 95%? 90%? 80%? How much Isp would you lose running at lower pressures like that?

Of course, a Merlin 1 doesn't have the same stringent requirements that drove the RS-25 design. It runs at a much lower pressure, and it uses a gas generator cycle rather than staged combustion. It has a very high T/W, but not stunningly high for RP-1. Assuming they had reuse in mind when they designed it, it's probably much easier to get to the level of reusability represented by the SSME Block III, or perhaps even better.

Part of the reusability comes from having fewer parts, and ya, not stressing them to ten tenths of capability. The T/W of the Merlin 1 d however is one of the highest for kerolox.

charliem · Post by **charliem** » Wed Oct 12, 2011 1:30 am

For the 1st stage at least, the distances and speeds that it'll have to deal with in order to land vertically are not that big.

I've been reviewing the videos from SpaceX and, extrapolating from them, at the separation of stage 1 Falcon 9 is traveling at a bit over 3 km/s, altitude ~120 km, and horizontal distance from the launch pad less than 200 km.

I don't think the horizontal distance is a mayor problem. They could just place the landing pad in the right place and that's it (although that'd rule out launches from Cape Canaveral, unless there is some island there I'm not aware of).

About the delta-V (and fuel) needed to take down gently, it's not that much either, just the terminal velocity for a body of that shape and mass. Don't know how to calc that but I bet it's subsonic. The Grasshopper RLV will only carry ~27 tonnes of fuel, and with that it's supposed to take off, reach 11,500 feet, come back, and land.

A bigger problem, I think, is stabilization and structural integrity. If that huge cylinder just goes down from 100+ km high tumbling at 3 km/s, surviving in one piece looks improbable.

The company said that their video simulation was not completely accurate, that they have left something out. Deployable fins maybe? Stabilization parachutes?

How about gyroscopes. How much mass they had to add to the present design to be up to the job?

Any aerospace engineer over here with clues for laymen like me?

P.E. It's 11,500 feet high enough for something like a Falcon 9 1st stage to reach terminal velocity (before crashing) if left there to free fall?

Ivy Matt · Post by **Ivy Matt** » Thu Oct 13, 2011 5:58 am

choff wrote:Apparently the latest Chinese launch propaganda video was playing 'America the Beautiful' in the background.

http://www.hindustantimes.com/Patriotic ... 52146.aspx

When asked why an American hymn was chosen, the state channel appeared to be stumped.

"I don't know how to answer your question," Chen Zhansheng of the CCTV propaganda department said. "I cannot help you."

He should have said, "Because it has such a beautiful melody. And besides, it's much easier to sing than 'The Star-Spangled Banner'."

Giorgio · Post by **Giorgio** » Thu Oct 13, 2011 6:22 am

charliem wrote:P.E. It's 11,500 feet high enough for something like a Falcon 9 1st stage to reach terminal velocity (before crashing) if left there to free fall?

No one apart from SpaceX can reply to this question.

D Tibbets · Post by **D Tibbets** » Thu Oct 13, 2011 4:40 pm

Landing the first stage down range, as opposed to the launch site would ease the fuel requirements considerably. As far as a gyroscope stabilizing the First stage, sure it's possible provided it was massive enough- thus the idea of spinning the entire rocket or tank. Using a small gyroscope to control flight control systems is reasonable but not actually directly maneuvering the stage.
A satellite might use a gyroscope/ reaction wheels to control attitude, but there are no external forces to overcome and time is not a major issue (fractions of a second vs minutes) so much less mass / torsional force is required to get the job done.

Does anyone know whether the helicopter RLV concept of a few years ago was abandoned for financial or technical reasons? Would it be more reasonable to incorperate it into a reusable first stage instead of a SSTO launcher?

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

Dan Tibbets

ladajo · Post by **ladajo** » Thu Oct 13, 2011 8:06 pm

I imagine auto-rotation is viable only at lower speeds and altitudes. It owuld be quite the engineering challenge to implement an auto-rotation system to withstand the kind of stresses we are talking about.