SpaceX SpaceX: First stage landed Satellites in orbit

[mfb]

How is this better then the parachute system used by the SRBs from the space shuttle?

The boosters were severely damaged by the impact and water and needed months of repair before they could be re-used. The vertical launch is much softer, and the hope is to re-use them within a day. Additional fuel is not an issue - fuel costs are negligible. It lowers the payload for a given rocket size, but if you have a Falcon Heavy or a small payload (and don't have to build a new rocket), this is not an issue.

 

[mheslep]

Fuel cost is almost negligible from what I understand. Someone mentioned the entire first stage fuel cost was just 0.7% of the total first stage cost. I can imagine a controlled landing at a pad being much more beneficial than a parachute wayer landing. Hot engine into salty ocean does not sound healthy.

It's not the fuel cost but the additional mass from additional fuel that is the issue. Payload mass is no more than single digit share of the total, so every additional kg of fuel (and tank and landing struts and ...) for boost back means a kg less of payload. The first step in this achievement was Spacex's breakthru reduction in vehicle mass (outer skin, turbo pump ,...), which then allowed fuel etc for a booster landing.

 

[mfb]

@mheslep: It is a bit better: payload has to go all the way to orbit, fuel for first stage return just has to get accelerated until the first stage engines cut off. That is a huge difference (~factor 5-10?).

 

[mrspeedybob]

How much difference would it make to have a landing pad on the balistic trajectory of the rocket at the time of separation, so that it doesn't have to reverse it's trajectory. Would this add significantly to the payload capacity?

I know this would require either a barge landing or a launch from somewhere other then Cape Canaveral. (Southern Texas maybe? With a landing pad in Florida)

 

[mfb]

I guess you'll have to ask SpaceX. They published some qualitative scheme a while ago, but without numbers. Something like:
Heaviest payload: Falcon Heavy, no reuse of anything, propellant cross-feed
A bit lighter: Falcon Heavy, landing of boosters
Even lighter: Falcon Heavy, landing of all three first stage elements, the middle one with some downrange distance
Even lighter: Falcon Heavy, landing of all three first stage elements close to the launch pad
Very light*: Falcon 9, landing of first stage

*still at ~13 tons to LEO, but very light compared to the 50 tons the first entry gives.

 

[LURCH]

Even watching it live, it didn't look real. That thing just came screaming down out of the sky, blasting flames. Then the flames went out, and I thought it had malfunctioned and was going to crash. Then the engines re-ignited, and the vehicle remained visible all he way down to the tree-line, where it still looked to be dropping too fast.

But it dropped out of site and no fire ball erupted, so that seemed to have gone ok. While I was still wondering if it had landed in one piece, there was this deafening double sonic boom, which made everybody jump; very reminiscent of the shuttle. Then someone watching the video feed said, "they did it; it's down safely!". We all cheered just like the folks at launch control. Never seen anything like that.

 

[mheslep]

@mheslep: It is a bit better: payload has to go all the way to orbit, fuel for first stage return just has to get accelerated until the first stage engines cut off. That is a huge difference (~factor 5-10?).

Rocket equation applies stage by stage. Two stage to LEO is 16.7% non fuel mass, ie rocket and payload, total all stages, +/- a bit depending on fuel choice. Doesn't leave much for payload.
https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#Examples

I think single stage rocket-only to orbit is impossible with chemical fuels?

 

[mheslep]

Even watching it live, it didn't look real. ...

:) A couple decades hence, people may look back on the Apollo parachute landings in the ocean, and say, that's nuts, does look real.

 

[mfb]

Rocket equation applies stage by stage. Two stage to LEO is 16.7% non fuel mass, ie rocket and payload, total all stages, +/- a bit depending on fuel choice. Doesn't leave much for payload.
https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#Examples

I know - so what? The second stage doesn't care about additional fuel in the first stage. 1 kg of remaining fuel in the first stage is like 1 kg of structural material in the first stage: you just need the "payload" (total second stage+payload mass) to total mass factor of the first stage, not the payload to total mass ratio of the whole rocket.

I think single stage rocket-only to orbit is impossible with chemical fuels?

Or at least so impractical that no one ever did it.

 

[Monsterboy]

I think single stage rocket-only to orbit is impossible with chemical fuels?

Or at least so impractical that no one ever did it.

Skylon's space plane which is currently under development can be considered as a single stage vehicle right ? Well it's not a rocket
https://en.wikipedia.org/wiki/Skylon_( spacecraft )

 

[mfb]

I guess you can count the various ideas of nuclear propulsion as single-staged as well. There are concepts, yes, but nothing that left the ground so far.

 

[cjl]

It's not the fuel cost but the additional mass from additional fuel that is the issue. Payload mass is no more than single digit share of the total, so every additional kg of fuel (and tank and landing struts and ...) for boost back means a kg less of payload. The first step in this achievement was Spacex's breakthru reduction in vehicle mass (outer skin, turbo pump ,...), which then allowed fuel etc for a booster landing.

I don't know that I'd call it breakthrough - the first stage of the Falcon has a full mass to empty mass ratio of something like 20:1, which, while very good, is hardly unprecedented. The Atlas LV-3B from the 1960s had close to 50:1, for comparison, though to be perfectly fair with that comparison, it's worth noting that the 50:1 is after it had dropped off some of its engines (and if you compare empty but with all engines to fully fueled, it ends up closer to 23:1).

 

[mheslep]

Not a comparable payload on the old Atlas, trading payload for fuel. Atlas was a couple tons, I think including the entire capsule. Falcon payload is 13 tons, not including the fairing etc. Falcon 1st stg empty now includes landing struts and aero fins. Lookin at a modern fully 2 stg Atlas, empty to full 1st stg ratio seems to be around 13.

 

[Dotini]

I'm glad the space age has finally caught up to where model rocketry was many decades ago.

In my distant youth, I designed and constructed a 4 stage model rocket, successfully launched, recovered, reloaded, relaunched and again recovered all 4 stages within 30 minutes.

I'd very much like to see man on the Moon again or on Mars. But I'm not optimistic that it'll be accomplished in the foreseeable future.

 

[Monsterboy]

The actual goal is to land the rocket at the same launch pad from where it launched right ?

 

[mrspeedybob]

The actual goal is to land the rocket at the same launch pad from where it launched right ?

I'd be doubly awesome if they could land the second stage on top of it, so that all they'd have to do between launches is re-fuel, and put another payload on top.

 

[mheslep]

I'm glad the space age has finally caught up to where model rocketry was many decades ago

Vice versa, now model rocketry can attempt to catch up to reality and attempt controlled landing using propulsion. I'm unaware of any thrust control used in model rocketry, but it would be required as in the real thing. Guidance on ascent makes use of an innately stable aerodynamic vehicle (fins that place the CP well aft of the CG). Modelers will have to raise their game considerably to match this.

 

[mheslep]

I know - so what? The second stage doesn't care about additional fuel in the first stage. 1 kg of remaining fuel in the first stage is like 1 kg of structural material in the first stage: you just need the "payload" (total second stage+payload mass) to total mass factor of the first stage, not the payload to total mass ratio of the whole rocket...

Yes, sorry, I missed your point in your earlier post.

 

[mfb]

The actual goal is to land the rocket at the same launch pad from where it launched right ?

The launch pad needs support structures that would be in the way for a controlled landing, so I doubt they will use the same pad ever. It's not that hard to move a rocket by a few kilometers, and you need access for some maintenance and putting the second stage on top anyway.

 

[cjl]

Not a comparable payload on the old Atlas, trading payload for fuel. Atlas was a couple tons, I think including the entire capsule. Falcon payload is 13 tons, not including the fairing etc. Falcon 1st stg empty now includes landing struts and aero fins. Lookin at a modern fully 2 stg Atlas, empty to full 1st stg ratio seems to be around 13.

Yes, because they decided balloon tanks are too much of a headache for the modern Atlas, so its structural fraction is worse. There are also quite a few other tradeoffs involved - I'd bet the modern staged combustion Russian engines the modern Atlas uses are quite a bit heavier than the old Atlas engines, for example, though they make up for that with their extremely high efficiency. As for the payload, I'm comparing the first stage's empty mass to its fully fueled mass - payload doesn't come into this at all. You have a valid point about the landing legs and aero fins though - I'm not sure if the number I found included those, and if so, how much those are contributing to the empty mass.

 

[enorbet]

I'm glad the space age has finally caught up to where model rocketry was many decades ago.

In my distant youth, I designed and constructed a 4 stage model rocket, successfully launched, recovered, reloaded, relaunched and again recovered all 4 stages within 30 minutes.

I'd very much like to see man on the Moon again or on Mars. But I'm not optimistic that it'll be accomplished in the foreseeable future.

Not to take anything away from Model (paper and balsa wood) or even Amateur (Stainless Steel and/or Carbon Fiber) Rocketry achievements but I think your first statement is rather hyperbolic :) it isn't even just a problem with scaling ie: Square-Cube Law but rather that the comparison is actually more Apples-to-Oranges, given that almost no Model rockets and very few Amateur rockets carry any payload at all excepting the body of the rocket which, in the case of Model rockets, doesn't even need to exist since it is possible to glue balsa fins directly on "the engine" as well as an (optional) nose cone and it will fly just fine.

The body is commonly, aside from appearance, just an aerodynamic housing for the parachute. In those few with actual payloads, eggs and cameras are the most common payloads of Model and Amateur rockets and even in those most advanced cases the rocket to payload ratio is extremely high, making parachute-only landings possible and relatively safe and easy.

This doesn't even address the vast differences in Mass and complexity once we leave the realm of "burn once" solid fueled devices, nor even the need for precision in all systems, not to mention guidance which is entirely static on both model rockets and amateur. Even recovery parachute deployment is left to a timed slow burn built-in the engine at the factory in the case of Models and little more than a mercury switch activated by Brennschluss in Amateur rockets. Nothing is optimized nor controllable beyond lighting the fuse. Timing is left to "good enough to work" with usually zero flexibility. All of this makes for a vastly reduced combination of mass and complexity so that no serious comparisons are possible, certainly of no value nor concern.

I do agree that putting men on Mars is likely a very long way off in time, but I'm betting Men on the Moon will occur within 10-15 years at the most, but neither has anything to do with any non-existent lag behind modelers.

 

[Monsterboy]

I'd be doubly awesome if they could land the second stage on top of it, so that all they'd have to do between launches is re-fuel, and put another payload on top.

Lol ,that will be too risky what if the first stage lands fine and the second stage crashes on top of it ?? it will be better if they land just a few hundred metres from each other near the same launch pad from where they were launched, because Elon said (in TED Talks) that the goal was to reuse the rocket within a matter of hours.

 

[Xu Shuang]

Aye. First time in history, right, from a full orbital launch?

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Only the first Stage rocket is recovered,which could cut the expense by half, at most.

 

[cjl]

Only the first Stage rocket is recovered,which could cut the expense by half, at most.

Why do you assume the first stage is only half the cost? It contains 9/10 of the engines, and something like 75-80% of the mass. I seem to remember hearing an estimate that the first stage was more than 75% of the overall cost of the launch vehicle.

 

[Blank_Stare]

Stage separation happened at 6000 km/h (and 77 km height), satellite deployment at 26000 km/h. That is 23%.
Full launch video
Vertical velocity seems to be more than 1km/s at that point. A very steep launch profile, but one that helps to get the first stage back to the launch pad.

Thank you for that link - very nice to watch.

 

[mfb]

The first stage is by far the most expensive part. You cannot buy them individually for obvious reasons, so there is no official price tag, but 75% or more sound realistic.
A factor of 4 won't give us all a nice holiday trip in an orbital hotel, but it is a huge step in the right direction.

 

[mheslep]

The first stage is by far the most expensive part. You cannot buy them individually for obvious reasons, so there is no official price tag, but 75% or more sound realistic.
A factor of 4 won't give us all a nice holiday trip in an orbital hotel, but it is a huge step in the right direction.

I expect the resulting increased launch rate will also reduce cost beyond that afforded by reuse of the stage.

 

[mfb]

It should. SpaceX has a really crowded launch schedule, 30 launches next year. Some of them will get moved to 2017 for sure (and some of the 2017 launches to 2018), but even 15-20 launches would be a lot.

 

[Xu Shuang]

Why do you assume the first stage is only half the cost? It contains 9/10 of the engines, and something like 75-80% of the mass. I seem to remember hearing an estimate that the first stage was more than 75% of the overall cost of the launch vehicle.

Based on the experience of space shuttles, recovering the first stage doesn't mean the cost of the first stage is gone. The first stage would still need serious renovation before reuse. For space shuttles, the engine need to be replaced every three missions. For the rocket, the renovation cost would be less, but would still be far from an ideal reuse.

 

[cjl]

Based on the experience of space shuttles, recovering the first stage doesn't mean the cost of the first stage is gone. The first stage would still need serious renovation before reuse. For space shuttles, the engine need to be replaced every three missions. For the rocket, the renovation cost would be less, but would still be far from an ideal reuse.

The space shuttles and this share very little though - the engine design is completely different, the resuse model is completely different, the fuel is completely different... It remains to be seen how much can be saved through reuse, but comparing this to the shuttle seems somewhat irrelevant to me.