Discussion SpaceX's Grasshopper RLV

[Urwumpe]

No offense, but I think the SpaceX engineers have a pretty good idea how to cut the costs to space.

Yes, and they have pocket calculators that are not always returning "by a factor 100" regardless what is calculated.

 

[T.Neo]

Fair enough, but I am going to commit heresy here and assert that the Space Shuttle was not re-usable and therefore a poor basis for making any judgments/assumptions on the matter.

Of course the Shuttle was reusable!

Parts of it were, anyway. It was just impractical to reuse them.

Reusability is the only way spaceflight will ever become routine.

STS was never 'routine'... :shifty:

 

[Mandella]

Where are they going to land first stage? After seperating from second stage it has ~3,5 km/s velocity. Killing that velocity with rocket engines and then building up some velocity to return to Florida would take at least 4 km/s deltaV which clearly is not feasible. Landing site in Africa would limit orbit inclination that can be reached and first stage can't cross Atlantic without additional boost. Landing on a ship would require extreme precision although it seems to be the most feasible from deltav perspective.

Landing it on a ship born pad would be no more difficult than landing it on a pad on the ground, given good weather and even seas. Of course, if it misses it'll be totally lost, and could even endanger the ship.

I'm really interested to see where they are planning to go with this.

 

[T.Neo]

What about recovery by barge, rather than a ship with people lots of expensive equipment aboard?

 

[Hlynkacg]

Of course the Shuttle was reusable!

Parts of it were, anyway. It was just impractical to reuse them.



STS was never 'routine'... :shifty:

Exactly, It was never reusable in the sense that a car or a plane is reusable, the turn around process was almost as involved as it would have been to build a new vehicle from scratch.

End esult is that you have a space craft that for all intents and purposes is expendable but with none of the advantages. ;P

 

[Urwumpe]

End result is that you have a space craft that for all intents and purposes is expendable but with none of the advantages. ;P

Yes, a prototype. Something that achieves the important goals, but requires further work to become something practically useful.

With todays technology and the STS experience, there could be a much better Mark II version of the Shuttle, but it would still be pretty much a completely new spacecraft in essence.

 

[C3PO]

Of course the Shuttle was reusable!

Parts of it were, anyway. It was just impractical to reuse them.

"Rebuildable" would probably be a more exact term.

One of the proposals to keep STS cost down was to stop reusing the SRBs. Building new ones was actually quite a bit cheaper then refurbishing flown SRBs.

 

[RGClark]

A couple of suggestions for the reusable version of the Falcon 9. First, model it on the DC-X. In the SpaceX video of the proposed reusable launcher the first and second stages have the same straight sides of the expendable versions. But having sloping sides helps to protect the sides of the vehicle during reentry as well as increasing aerodynamic stability during reentry.
Note that as long as the cross-section remains circular for a conical shaped stage you should still get the high tankage ratio that obtains for cylindrical tanks:
...
The second model for the reusable Falcon 9 stages would be on the ESA's proposed Intermediate eXperimental Vehicle (IXV):

Article:
Europe Aims to Launch Robotic Mini-Shuttle By 2020.
Rob Coppinger, SPACE.com ContributorDate: 13 June 2011 Time: 02:58 PM ET
http://www.space.com/11948-robot-space-plane-europe-ixv-launching-2020.html

This does not use the powered landing of the DC-X but rather uses a glided landing via its lifting body shape. SpaceX does not like the use of wings for landing because of the extra weight. But this design would not have wings. It would have larger thermal protection weight because the horizontal underside would have to be covered, whereas in the DC-X mode only the base has to be covered. However, it would make up for this in not requiring fuel for the powered landing.
In this case because the stages would have to maintain the aerodynamic shape, they could not be stacked as for serial staging. Parallel staging would have to be used. Once again this means the separate stages could be used as SSTO's.

Another possible lifting-body shape for reusable Falcon 9 stages might be of the Japanese HYFLEX hypersonic test vehicle:

Hypersonic Flight Experiment "HYFLEX".

http://www.jaxa.jp/projects/rockets/hyflex/index_e.html

HYFLEX.
http://www.rocket.jaxa.jp/fstrc/0c02.html

This was successfully tested all the way back in 1996 at a Mach 15 reentry speed.
It's roughly cylindrical shape would mean you would lose a relatively small degree on the mass efficiency of cylindrically shaped tanks. However, rather than redesigning the tanks you might want to just use a composite aeroshell on the usual Falcon 9 stages. A conical aeroshell for example was used on the DC-X.
This would make the reusable Falcon 9 more quickly and easily to be implemented. The mass of the aeroshell though would contribute to the mass lost from payload.
As with the above cases, used with altitude compensating nozzles on the Merlins or with existing high efficiency engines with just their standard nozzles, these HYFLEX-shaped stages could also be SSTO's.

Bob Clark

 

[T.Neo]

Did anyone see a HYFLEX-like lifting body in the SpaceX video? Anyone? I didn't, did I miss something?

Also, RGClark... remember the limitations of "altitude compensating nozzles"... nine Merlins fit on the first stage, but a single MVac fills the entire interstage. If you need more thrust and you need more engines, you won't be able to fit the nozzle extensions in.

And even then, what sort of performance would you get? In the range of F1, F1e? An F9-derived vehicle would be quite massive for a vehicle able to lift only a ton to LEO.

 

[RGClark]

Did anyone see a HYFLEX-like lifting body in the SpaceX video? Anyone? I didn't, did I miss something?

Also, RGClark... remember the limitations of "altitude compensating nozzles"... nine Merlins fit on the first stage, but a single MVac fills the entire interstage. If you need more thrust and you need more engines, you won't be able to fit the nozzle extensions in.
And even then, what sort of performance would you get? In the range of F1, F1e? An F9-derived vehicle would be quite massive for a vehicle able to lift only a ton to LEO.

Elon doesn't like wings because of the added weight. However, a lifting body does not add wings. The assumption may have been a glided landing would have required wings so they didn't consider it.
I have mentioned there are possibilities for lightweight altitude compensation. I'll write about those in the next day or so.


Bob Clark

 

[orb]

Parabolic Arc: FAA Assessment Clears Way for SpaceX Grasshopper Tests

 

[orb]

NASASpaceflight: SpaceX to begin testing on Reusable Falcon 9 technology this year:

Space Exploration Technologies Corp. (SpaceX) will begin testing on a vertical propulsion landing system later this year, part of a long-term project to evaluate the potential of creating a fully-reusable version of their Falcon 9 launch vehicle. SpaceX believe a fully and rapidly reusable orbital class rocket would provide a critical breakthrough for the human race’s ambition of becoming a multi-planetary species.

{...}

 

[TaylorR137]

Launch from Texas. Land stage 1 in Florida. Bribe the Florida politicians to grease the legal skids. Early shuttle studies considered the Texas coast as a new launch site.

http://www.space.com/15220-spacex-rockets-texas-launch-site.html

WASHINGTON — Details about a launch facility Space Exploration Technologies Corp. (SpaceX) is considering building in Texas emerged April 9 in a Federal Aviation Administration (FAA) document detailing an environmental review that must precede construction.

The proposed launch site would be used “to launch orbital and suborbital launch vehicles from a private site in Cameron County in southern Texas,” according to the FAA’s notice of its intent to prepare an environmental impact statement. All launches from the proposed spaceport would fly east over the Gulf of Mexico, the document said.

The proposed Texas facility would be built to handle up to 12 commercial launches a year and would support SpaceX’s Falcon 9 medium rocket and the company’s planned Falcon Heavy launcher for which SpaceX has no paying customers. Falcon 9 launches from the proposed facility would include launches of the Dragon space capsule, which SpaceX plans to begin launching this year from Cape Canaveral Air Force Station, Fla., to fly cargo to the international space station under a $1.6 billion contract with NASA.

Looks like you called it on the Texas launch site.

 

[T.Neo]

One wonders what rationale there is behind the third launch site. SpaceX seems to be 'predicting' quite high launch rates- repeat of Saturn/Titan/Shuttle/EELV pattern?

 

[Capt_hensley]

Gateway Station has a sustained launch rate of about 150 rockets over 5 years. Although GWS is fictional, that's what it would take for such a huge project. That's 2.5 rockets every month on average.

Who's to say the MARS dream isn't part of the ambitious launch site prep. It could happen!

 

[RGClark]

SpaceX Grasshopper nearing first test flight.

Just saw this on Hobbyspace.com:

Reusable rocket prototype almost ready for first liftoff
BY STEPHEN CLARK
SPACEFLIGHT NOW
Posted: July 9, 2012
http://www.spaceflightnow.com/news/n1207/10grasshopper/


Bob Clark

 

[orb]

Spaceflight Now: PHOTOS: Grasshopper reusable rocket demo

 

[John_L]

That's something in the video I found odd. Of course you can land the Dragon anywhere you want that your orbit will pass over, and if you have the cross-range capability (shades of STS) you can land the upper stage at the launch site after one orbit if you resolve the TPS and weight problems, etc. But how does the first stage get back to the launch site? It's trajectory is sub-orbital, so it's not going once around and landing. Unless they intend to land it someplace else and the KSC landing in the video is "for illustration purposes only."

He talks about that in the video, he says it's a common misconception that you need wings for lift, but basically, he said you'd do a burn to lower delta v, then using the vehicle itself as a "lifting body" of sorts, you can, once slowed down, get the stage back to the launch site and then have a propulsive landing back at the pad. He said they've got it working "on paper", which, as we all know, reality never is exactly like it is on paper, but, they feel confident they can do it.

As far as saying weather it can or cannot be done... well, Elon's been continuously bombarded with criticism from the go. They said he'd never launch a rocket into space... done, they said he'd never get F9 off the ground... done. They said he'd never recover a craft from orbit... done. They said he'd never make it to ISS.... done.

So... I may not be the brightest bulb in the pack, but if we're takin' bets.... I'm going to go with "I think he'll pull it off".

If any can, it's SpaceX and Musk.

 

[N_Molson]

It is technically possible, but I'm still a bit sceptical about the payload-efficiency of the thing... If you can basically just refuel the vehicle and launch it again it can be ok. But if an in-deep refurbishment is needed, it kills the concept IMHO. That can only be established by experience.

 

[orb]

Elon Musk via Twitter:

First test flight hop of our Grasshopper VTVL rocket! http://twitter.yfrog.com/0wusutopshpepnbpmodbgnosz