Automated first-stage landing

[pavelcherepan]

Below is the link to Youtube video on unsuccessful (yet again) landing of the first stage of SpaceX's Falcon 9 rocket. The craft managed to successfully approach the landing pad but in final moments of landing sequence excess horizontal velocity resulted in it falling on its side and exploding. In the very final moments you can see the RCS thrusters on the top of the vehicle working hard, but still they couldn't stop it from falling:

 

https://youtu.be/GbYQQE5LZ2E

 

Anyway, I'm generally really supportive of what Mr. Musk and his team are doing and this technology seems like a very important advancement in attempting to make space flights cheaper. Obviously I don't have the required information (which only SpaceX has) but still gets me thinking of how big are the chances of successful landing this way.

 

It seems to be easier for spaceplanes (although they are generally much less cost-efficient) to perform automated landing since they have some reasonable amount of lift. For example, Space Shuttle on approach has lift/drag ratio of 4.5, which is actually more than Concorde has. This allows them to possibly make more than one attempt to land if conditions are unfavorable. I think I read somewhere the Buran shuttle on its first and only flight landed automatically on second attempt due to strong cross-winds (it's claimed to have L/D of 6.5).

 

Do you think that this technology is here to stay or it will be temporary and will be abandoned soon?

[EdEarl]

I think Elon Musk is technically competent and an astute businessman; thus, I believe he will master the landings, refurbish the rockets economically, and reduce the cost of putting things in space.

[Enthalpy]

- Failure belongs to trying and innovation. Those who claim "working at first shot" have never innovated.

- Three failures are nothing exceptional. Remember the attempts before Von Braun could handle the space program.

- Failures at landing cost to SpaceX, no to the customer, so it's their business.

 

A plane is full of handicaps.

- It needs wings, a landing gear, possibly engines, and this goes frontally against the optimization a launcher needs.

- A first stage separates 500-3000km downrange the launching pad which uses to be at the coast, so it can't glide back like the Shuttle or Buran (no engine). It needs an engine, possibly of different technology, maybe a different fuel.

- Flying needs to integrate in the air traffic. Airworthyness, flight routes, all the mess. That must be very difficult in Florida or California. You can't just let a thing fly through the air.

 

Because of this, I consider SpaceX's platform in the Ocean a re-brilliant idea. I couldn't imagine landing on the continent, but downrange on the Ocean it gets reasonable. To my opinion, this is the definitive scenario, not a provisional one as claimed.

 

A big part of the cost advantage of Falcon 9 is that it achieves Leo and Gto with two stages only and one motor type. Any handicap at the first stage wreak havocs that: wings and landing gear, solid propulsion, air-breathing engines...

 

Resulting from the thoughts above, my proposal for a re-used first stage is a pressure-fed liquid that splashes in the Ocean
http://www.scienceforums.net/topic/65217-rocket-boosters-sail-back/#entry847336

United Launch Alliance wants to catch only the engine under a parachute from a helicopter

and SpaceX lands on a platform. This makes three reasonable scenarios where the stage falls over the Ocean. Until I see something else, I consider scenarios where a stage joins the launch base through the air as inferior if feasible.

 

And, yes, a technically competent boss changes everything.

[pavelcherepan]

 

 

Because of this, I consider SpaceX's platform in the Ocean a re-brilliant idea. I couldn't imagine landing on the continent, but downrange on the Ocean it gets reasonable. To my opinion, this is the definitive scenario, not a provisional one as claimed.

 

Actually, I've read that for the next launch they will try and land the first stage on land ( EDIT: I checked, this is not a tautology )

 

 

 

President and COO Gwynne Shotwell said that the company hopes to land the rocket on ground rather than at sea.

 

 

 

 

Resulting from the thoughts above, my proposal for a re-used first stage is a pressure-fed liquid that splashes in the Ocean

http://www.sciencefo...ck/#entry847336

 

Thanks for that. I've been also wondering for a long time why no one ever tried to land first stage on parachutes? We do drop tanks from planes on chutes so it shouldn't be impossible to do with a first stage.

 

I've never thought of paraglider though, this is new to me.Do you know if any tests for systems like this have been attempted? Seems much easier than using engines for a controlled landing.

 

 

A plane is full of handicaps.

- It needs wings, a landing gear, possibly engines, and this goes frontally against the optimization a launcher needs.

- A first stage separates 500-3000km downrange the launching pad which uses to be at the coast, so it can't glide back like the Shuttle or Buran (no engine). It needs an engine, possibly of different technology, maybe a different fuel.

- Flying needs to integrate in the air traffic. Airworthyness, flight routes, all the mess. That must be very difficult in Florida or California. You can't just let a thing fly through the air.

 

I agree. All of these are highly detrimental, unless SSTO design is developed (which AFAIK is near impossible on Earth). But then another question: some planes utilize variable wing geometry. Could this design be of any use for re-usable space vehicles?

Edited April 18, 2015 by pavelcherepan

[Enthalpy]

Land under a parachute:

- Most boosters do it. The Space Shuttle did splash them in the Ocean. There they sank after some days, the cavity filed with seawater, they stayed vertical at the beginning. All that made recovery difficult, and the planned reuse was abandoned.

- Pressure-fed liquids would do that better: the tanks are closed, they stay dry and clean, the booster or first stage swims horizontally, their tick steel is already seaworthy.

- It has been done on land for orbiters, without propulsion, under a paraglider, landing outside an airport. But a booster can't glide back to the continent.

 

A propulsive kite (for a booster, the paraglider in an additional role) is used on cargo ships to save fuel. Fully automatic.

http://www.skysails.info/english/

 

Ssto are perfectly feasible from Earth. The numbers are favourable, and have been for decades. But why?

- They would reach Leo, not Gto nor Geo.

- If a launcher is thrown away, I care little whether it's in one or two pieces. I prefer to reuse its first stage or both than throwing it away in one piece.

- They demand engines that throttle very deeply. This big difficulty is forgotten by many proponents.

- I don't believe Ssto and reuse are compatible, using present technology.

- A second stage isn't so costly, especially if it uses the same engine (Falcon 9), and improves the performance.

- A better goal would be to reach Leo by the launcher, so the satellite needs faint electric propulsion only, and is there in few days, not costly months. Two improved hydrogen stages to Geo are easier than one to Leo, more efficient, more useful. Three kerosene stages to Geo would be easy and very efficient, better than two overstretched kerosene stages to Gto followed by electric propulsion.

 

Variable wing geometry is proposed (a model was displayed) for a kerosene booster pushed by an RD-191. Their clever design uses a scissor wing, parallel to the body as a rocket, perpendicular to the flow as an airplane. Though, I'm not convinced by wings, landing gears, atmospheric engines: heavy, incompatible design constraints, integration in the air traffic.

[pavelcherepan]

 

 

Ssto are perfectly feasible from Earth. The numbers are favourable, and have been for decades. But why?

 

I'm straying off-topic here but from what I've seen they aren't feasible at the moment largely due to structural limits of current technology. For example, this graph from wiki article shows that SSTO is only capable of getting to LEO (9.1 km/s delta-v, payload 4500 kg) with a specific impulse of 450 s, which we can't achieve (at sea level) with current fuels based on this data. Of the currently used drives only the ion drives can achieve that sort of SI but their thrust is far too low to use them to launch from the surface.

 

 

 

[michel123456]

 

Actually, I've read that for the next launch they will try and land the first stage on land ( EDIT: I checked, this is not a tautology )

 

 

Landing on ground is a better concept IMHO. I get the impression that the thruster is destabilizing the floating platform and that may be a reason for the failure.

 

And i hope the deisgners have in mind to keep the center of mass of the (empty) rocket as low as possible, near its basis. it is so fundamental that i believe they did.

The other way round would be to land into a big hole, or a large cylindrical structure.

 

------------------

The 1km test went right

https://www.youtube.com/watch?feature=player_detailpage&v=EuP6Uk-0S4c

 

The 325m test is even more impressive.

Edited April 18, 2015 by michel123456

[Enthalpy]

[...] this graph from wiki article shows that SSTO [...]

 

You can forget that Wiki article. There is no single reason to set a structural coefficient at 0.1.

 

For instance, the Shuttle's external tank weighed 36kg per ton of propellants. These were hydrigen+oxygen, and the tank was structural, since the solid boosters pulled it at its top and it pushed the orbiter at its base, and all that, widely off-axis. The SLS has an equally good central hydrogen+oxygen stage (said to derive from the Shuttle). Add some engines, plus some electronics from the cell phone era, you get 70kg/t.

 

This is a traditional and unfavourable way of building tanks. Other options, like balloons in a truss, would do better. Carbon fibres too, when operational soon. Then we drop to 50kg/t with hydrogen. A small launcher would make this easier.

 

Don't take braeunig's article litterally. The Isp is a standard value from a bad expansion ratio that make simple Psi figures and was credible in 1950. Kerosene engines flown in 1980 achieve 308s at sea level, 338s in vacuum - and more with wider nozzles.

 

Then, the isp that counts most is the vacuum one, almost to 90%. Starting an engine at ground level reduces its thrust, annoying for an Ssto, and limits the nozzle diameter to about 0.3 bar expansion hence the Isp - BUT a simple nozzle insert dropped at altitude permits a much wider nozzle and a better liftoff thrust, easing an Ssto much.

 

You could also consider kerosene. Thanks to density, the tanks get easier to build despite the lower Isp needs them lighter. The real drawback is that the engine must throttle even deeper than with hydrogen.

 

So, if you put the proper numbers together, an Ssto really is no big difficulty apart from throttling. The true argument against is "why" and "what benefit".