The Reaction Engines Skylon Master Thread (1)

[flymetothemoon]

Elon Musk continually refers to stages when asked about these questions.

"air breathing hybrid stages"

"You could just make the boost stage 5% to 10% larger"

It seems clear he is not talking about Skylon or Sabre and probably doesn't know much about them. Would you agree?

[flymetothemoon]

Elon Musk continually refers to stages when asked about these questions.

"air breathing hybrid stages"

"You could just make the boost stage 5% to 10% larger"

It seems clear he is not talking about Skylon or Sabre and probably doesn't know much about them. Would you agree?

If this is true, what would be very interesting is if we were clear that he really did know the technologies in detail and *then* he answered the questions.

[flymetothemoon]

In any case I would very much like to think the following is true and that the world can benefit from a real win-win.

I don't think Reaction Engines would be a threat to Musk in any case. He is going for much larger vehicles so will be able to create and address different markets in timeframes any Skylon derived vehicle couldn't possibly match e.g. some future Jumbo-Skylon.

I think, if SpaceX achieve re-usability, over time, the two approaches would prove to be complementary and market-dominating. Being different sorts of vehicles, they will be able to solve different sorts of problems. providing lots of excellent opportunities for space applications going forward.

[john smith 19]

I don't think Reaction Engines would be a threat to Musk in any case. He is going for much larger vehicles so will be able to create and address different markets in timeframes any Skylon derived vehicle couldn't possibly match e.g. some future Jumbo-Skylon.

I think, if SpaceX achieve re-usability, over time, the two approaches would prove to be complementary and market-dominating. Being different sorts of vehicles, they will be able to solve different sorts of problems. providing lots of excellent opportunities for space applications going forward.

It's possible. There is an REL study for a Mars mission called Project Troy, which you could loosely describe as "flexible path," REL style.

Note that when Elon was spec'ing his LV company the bulk of all payloads had got to orbit by multi stage ELV. The exceptions were Atlas II (discard some engines, but few went up without a 2nd stage anyway, about 1.7x the Delta 2 payload at 2.5x the cost), STS (Big SRBs + big drop tank), Buran (drop all main engines with the booster) and Pegasus (aircraft 1st stage and a minimum of 3 more solid stages under a wing and IIRC the highest $/Kg of any launcher)

So if you're looking to get into the launch business with minimum initial risk of failure and a shot at low(ish) launch costs and (later) re-usability what design would you go for?

There are and have been many launch architectures proposed. Skylon stands out in that (after a long time) it has started to get funding.

[Lars_J]

There are and have been many launch architectures proposed. Skylon stands out in that (after a long time) it has started to get funding.

What is the current funding situation?

[ArbitraryConstant]

It seems clear he is not talking about Skylon or Sabre and probably doesn't know much about them. Would you agree?

He might just prefer not to call them out specifically. He probably does know they're out there, but it's entirely possible to try some back of the envelope calculations to see how big a win it would be if someone could make it work even if you don't know about them.

Eg, even if you don't know about sabre, imagine a hypothetical engine that's really amazing and compare it to just building a bigger stage.

[QuantumG]

Or you could just have two stages...

...which significantly increases both development and operation costs. Why use staging when you have free oxidizer ?

What's the weather like on your planet?

[Longstaff]

SpaceX are planning massive, expendable vehicles, which may over time evolve to be partially reusable (but with a lower payload fraction). Reaction Engines are planning a fully reusable aircraft that is large, but lighter than a Boeing 747 at take-off, and much lighter than an Airbus 380.

Skylon is also planned to have a higher payload fraction than an expendable, and a lower sensitivity to mass growth (93413 hit the nail on the head - it is all a question of effective specific impulse, and a trade-off between drag and gravity losses).

[tlesinsk]

What's the weather like on your planet?

Oxygen-rich.

[john smith 19]

...which significantly increases both development and operation costs. Why use staging when you have free oxidizer ?

What's the weather like on your planet?

You can develop 2 stages (including all analysis and development costs) for the price of 1?

I'm fascinated. Please explain.

[QuantumG]

...which significantly increases both development and operation costs. Why use staging when you have free oxidizer ?

What's the weather like on your planet?

You can develop 2 stages (including all analysis and development costs) for the price of 1?

I'm fascinated. Please explain.

No thanks.

Go read a book.

[Rugoz]

I guess skylon will still be "nearly full" when it switches to rocket mode, so I don't expect big benefits from making it two stage. Also it must withstand temperatures of ~500°C at mach 5 anyway.

Maybe a suborbital skylon with expendable upper stage for GTO launches could make sense, however I think REL should aim for the orbital tourism market.

[93143]

They're aiming for the geostationary comsat market, for a start.  That's how they sized the vehicle and its reusable upper stage.

You can do a suborbital deploy and expend the upper stage, but it's expensive; the payload to LEO doubles, but the cost per kg is still higher because you've just tossed a $70M upper stage.  (Though I suppose you could use a stage that was about to be retired...)  To improve the payload to GTO with suborbital deployment you'd have to develop a bigger stage, because the current plan is to deploy it full in LEO.

[Turbomotive]

I suppose you could use a stage that was about to be retired

That's a neat trick - every 10th launch you get an expendable payload for the price of a reusable?

[tnphysics]

Also, there is no reason (IMO) that the LEO stage could not be reused, if the orbital mechanics worked out. The key would be for the LEO stage to stay in an orbit where a future Skylon on another mission (LEO payload only?) could retrieve it in passing. Also, on some missions (such as to escape, unless the spacecraft acts as 3rd stage), the upper stage is non-reusable anyway, so suborbital deployment might make sense, IF the upper stage is given extra (stretched?) tankage for the mission.

[anonymous]

SpaceX are planning massive, expendable vehicles, which may over time evolve to be partially reusable (but with a lower payload fraction).

SpaceX are planning full reusability.

http://www.nasaspaceflight.com/2012/01/spacex-testing-reusable-falcon-9-technology-this-year/

[grondilu]

SpaceX are planning full reusability.

http://www.nasaspaceflight.com/2012/01/spacex-testing-reusable-falcon-9-technology-this-year/

Of course they are.  Musk talks about it whenever he can.


And they regularly show us their grasshoper tests:



SpaceX and ReactionEngines have reusability as a common objective.   But that's about all they have in common.

In a nutshell:

	SpaceX	ReactionEngines
Reusable?	Yes	Yes
stages?	Multiple	Single
wings?	Nope	Yes
Breathing air?	Nope	Yes

[Turbomotive]

SpaceX are planning massive, expendable vehicles, which may over time evolve to be partially reusable (but with a lower payload fraction).

SpaceX are planning full reusability.

http://www.nasaspaceflight.com/2012/01/spacex-testing-reusable-falcon-9-technology-this-year/

here from that article

the obvious challenge of potentially trading some of the vital upmass ratios, via the extra mass required for the additions to enable the launch vehicle to become reusable

on top of designing, building and testing all the kit as well..

It may well work, but still seems inelegant compared to a space plane.

[simonbp]

SpaceX and ReactionEngines have reusability as a common objective.   But that's about all they have in common.

And that's good thing. If even a single style of RLV succeeds, then the market will grow enough to support many. Economic forces will then determine the most efficient methods. Time will tell if Skylon is a Comet or a 707...

The next decade is going to be quite exciting.

[BobCarver]

check this page.
http://www.reactionengines.co.uk/sabre_howworks.html
click on the 3rd picture.

John,

Thanks. I thought embrittlement was still an issue, but apparently I was mistaken. Thanks for that reference.

And, Elon Musk was obviously addressing an air-breathing, vertical ascent rocket stage in his talk, not SKYLON. I doubt he even has read anything about REL. He didn't even understand the tradeoff between gravity losses and a winged vehicle. Apparently, he's too busy to keep abreast of what the competition is doing. His argument against an air-breathing rocket falls flat on its face when you realize he's reasoning from a viewpoint of ignorance.

It just shows that even a genius like Musk can be wrong based upon ignorance.