SpaceX SpaceX: First stage landed Satellites in orbit

[cjl]

The ISS and Shuttle provide a lot of habitation capability, for long to very long term. Capsules not so much. So, for example, in a future with not ISS, no Shuttle, what to do with a crew in a capsule that's disabled for some reason and can't re-enter. Or, how does one accomplish a two week service mission on some orbital instrument like Kepler, requiring multiple EVAs in large maneuver packs and requiring some kind of capture (as with the Shuttle arm)?

All the speculative designs I've seen involve having some habitation area that is not designed for reentry, and the capsule itself is just used for reentry (and it would detach shortly before the reentry occurs). As for service missions, most current satellites are not designed to be serviceable, and in most cases (including Hubble, at least by some estimates), it is cheaper to just launch an entire new satellite rather than trying to service an existing one. However, if you really needed to service one, again, send up the tools needed to service the satellite (and possibly also a long-term habitation area) with the capsule, and the overall payload requirements will still be less than for a shuttle-like vehicle.

 

[mfb]

The ISS and Shuttle provide a lot of habitation capability, for long to very long term. Capsules not so much. So, for example, in a future with not ISS, no Shuttle, what to do with a crew in a capsule that's disabled for some reason and can't re-enter. Or, how does one accomplish a two week service mission on some orbital instrument like Kepler, requiring multiple EVAs in large maneuver packs and requiring some kind of capture (as with the Shuttle arm)?

The ISS is a backup option for a very narrow range of orbits only. A space shuttle that cannot re-enter would have had the same problem.
3 tons of payload can support a crew for quite some time.
No idea about robotic arms.

I haven't seen any discussion about an obvious application of this technology for a Mars mission. That being, some sort of large rocket will be needed, on Mars, to get our people off of Mars and on their way home. The ability to land a large rocket in a condition which is almost immediately re-usable seems like a prerequisite accomplishment for the Mars mission.
How much of the technology developed to land the first stage of the Falcon form sub-orbital altitude and velocity on Earth, will be applicable to landing a complete, and fully fueled, and ready to use rocket on Mars from Martian orbit?

The launch payload would be a single capsule with humans and a few rock samples, if we use a Dragon v2 this is about 5 tons. Mars surface to orbit just needs ~3.5 km/s (plus <10% for gravity drag), that is significantly below the capacity of the second stage of Falcon 9. Using this second stage without modification but with less fuel, we get another 4 tons of structural mass, the specific impulse of 340 seconds would suggest a lauch mass to dry mass ratio of ~3, so we need an estimated 27 tons on Mars, maybe a bit more. This happens to match the dry mass of the first stage (26 tons). The current second stage doesn't have landing gears, but we did land something of that mass on Earth with 3 times the surface gravity.

Cross-check: The second stage has a maximal thrust of 800 kN, sufficient to accelerate 27 tons by 32 m/s, or roughly 10 times the Martian surface gravity.

All SpaceX-related numbers from this page.

 

[Monsterboy]

http://www.nbcnews.com/tech/innovat...acex-falcon-9-rocket-ready-fire-again-n488926

Elon says the first stage is 'ready to fire again' but...

Though this particular history-making rocket appeared to be unscathed, Musk has said it's unlikely to be used for another mission and will probably be put on display instead.

"I think we'll probably keep this one on ground," Musk said after the landing. "Just because it's kind of unique, it's the first one that we've brought back. So I think we'll probably keep this one on the ground, but just confirm through tests that it could fly again."

 

[HyperTechno]

What about the cost of fuel used on landing the 1st stage back on ground? and also the cost of repairs?
aren't they expensive more or equal to the cost of building a new 1st stage?

 

[Monsterboy]

What about the cost of fuel used on landing the 1st stage back on ground? and also the cost of repairs?
aren't they expensive more or equal to the cost of building a new 1st stage?

No , that's the whole point of a reusable rocket ,the cost of fuel is very very less compared to the cost of the rocket ,this has been made clear earlier in this thread , the cost of repairs will also be very less compared to building a new rocket unless something goes wrong and the rocket crashes (in this case i don't think it can be repaired).

 

[mfb]

What about the cost of fuel used on landing the 1st stage back on ground? and also the cost of repairs?
aren't they expensive more or equal to the cost of building a new 1st stage?

See the previous posts, fuel is below 1% of the launch costs, and the additional fuel needed to get back is a small fraction of this 1%. The repair costs will need more long-term experience to get a reliable estimate, but the goal is to have it ready for flight within hours, so basically no repairs necessary.

It is really similar to an airplane - building a new one for each flight would be ridiculous even if you have to fly the existing airplane back empty.

 

[cjl]

See the previous posts, fuel is below 1% of the launch costs, and the additional fuel needed to get back is a small fraction of this 1%. The repair costs will need more long-term experience to get a reliable estimate, but the goal is to have it ready for flight within hours, so basically no repairs necessary.

It is really similar to an airplane - building a new one for each flight would be ridiculous even if you have to fly the existing airplane back empty.

Well... it's not quite that simple, unfortunately. The rocket does need to be bigger and heavier to lift the same payload, since it now needs to carry the extra fuel and equipment to allow the stage to return and land, and the launch profile used for this flight (and presumably all reusable flights) is rather different than what you would normally want (it was fairly lofted, with the first stage giving the rocket less overall delta V and downrange distance than you normally would). This trajectory required the second stage to be larger and more powerful than it would otherwise need to be to make up for the shortfall in downrange performance from the first stage. Since the second stage is not reused, any additional performance from the second stage is still rather expensive. However, despite these tradeoffs, SpaceX still believes they can save a lot of money through the boostback, and I would tend to believe them on that. I just want to point out that there are some other considerations on top of just adding the cost of the extra fuel for the boostback though.

 

[mfb]

The second stage has a fixed size, SpaceX cannot use a smaller one. Yes, returning to the launch pad reduces the maximal payload, but the payload was light enough to allow such a mission. Heavier payloads will have the first stage land on the drone ship, and even heavier ones get an expendable rocket (or move to Falcon Heavy in the future). That's something I wrote at least 5 times now in this thread. The Falcon 9 is cheaper than many smaller rockets - even without the re-use feature.

 

[cjl]

The second stage has a fixed size, SpaceX cannot use a smaller one. Yes, returning to the launch pad reduces the maximal payload, but the payload was light enough to allow such a mission. Heavier payloads will have the first stage land on the drone ship, and even heavier ones get an expendable rocket (or move to Falcon Heavy in the future). That's something I wrote at least 5 times now in this thread. The Falcon 9 is cheaper than many smaller rockets - even without the re-use feature.

The second stage has a fixed size, and that fixed size is larger than it would be if they had designed the rocket to be disposable while still carrying its' typical payload capacity. It's true that the design is fixed now, but the whole rocket design was based around the concept of reusability, so you can't just claim that everything would be the same size (and cost) if they had designed it as a disposable rocket from the start.

 

[mfb]

The baseline so far is a disposable rocket. The re-usable version is a modified first stage. A bit heavier and with a lower payload capacity. Well, "lower" - the Falcon Heavy will beat the heaviest operational system (Delta IV Heavy) by nearly a factor 2 (and cost ~1/4 per launch). Even with re-use of all three cores, it will have a higher payload capacity than all other rocket systems currently in use.

 

[cjl]

The baseline so far is a disposable rocket. The re-usable version is a modified first stage.

Yes, but the Falcon 9 was designed from the start with reusability in mind, and many of the design decisions were based around that, especially if you look at the "V1.1" and newer variants (which were a pretty heavy redesign compared to the originals). If you designed a rocket from scratch for disposability, it wouldn't necessarily end up with the same set of compromises.

Oh, and as for the FH, I'll believe the cost numbers when it's operational, though I do hope it delivers on its promises.

 

[mfb]

Well, they did sell some FH launches already, and the Falcon 9 costs are quite low as well.

 

[Monsterboy]

Since the second stage is not reused, any additional performance from the second stage is still rather expensive. However, despite these tradeoffs, SpaceX still believes they can save a lot of money through the boostback, and I would tend to believe them on that. I just want to point out that there are some other considerations on top of just adding the cost of the extra fuel for the boostback though.

I am not an expert but the problem you stated will disappear if the second stage is also made reusable right ? SpaceX's goal is to develop a fully and rapidly reusable rocket right ? So even if the payload capacity is reduced to a small extent due to the additional fuel and equipment ,the fact that the same stages are supposed to be reused several times reduces the cost over many launches IMO.

 

[mfb]

The second stage won't be reused for the current Falcon 9: Interview with Elon Musk. A following generation of launch vehicles could try that (also discussed in the video).

 

[mheslep]

Interview with Elon Musk.

Great discussion. I'm curious about some of the other issues he raises in that interview, such as the assertion that commercial e-aviation becomes viable with a one-third improvement to battery energy density, from 300 Wh/kg to 400 Wh/kg. Then there were his concerns about the power required for beam based space launch.

 

[mheslep]

Then there were his concerns about the power required for beam based space launch.

Musk said the beamed power required might be equivalent to the whole "east coast". Let's see.

Assume the beamed power was to replace, say, the 1st stage of a Falcon 9, and to lift the second stage mass to the usual 1st stage separation point (MECO). Separation of this most recent launch was at V=~1700 m/s. Mass of the second stage is about 100 mtons. So, excluding efficiency and drag, lift power over 300 secs to achieve Vmeco is ~1/2 GW. With, I dunno, a ~25% efficient transmitter, and the same on the receiver, the ground power must be 4 GW for 5 mins. On the ground, dissipating 3 GW of heat requires a large power plant sized cooling system. For stored energy, five minutes is in the flywheel range. The flywheel company Beacon Hill made 265 kW units with exactly 5 mins of run: about 15100 units gives 4 GW. Recharge and launch every few hours or so, depending on the grid connection. About $800 million at 20 cents/Watt for the flywheel array.

 

[cjl]

How are you going to convert 100% of the received energy into kinetic energy of the craft though?

 

[mheslep]

How are you going to convert 100% of the received energy into kinetic energy of the craft though?

I assumed 25% at the receiver, wild guess. Several conversion ideas have been kicked around for years, about which I know little. Ablative, pulsed or CW plasma, etc.

A live demo and a bit of hype here:

 

[mfb]

Nearly all those concepts (and in particular, all with a reasonable efficiency) require some propellant to be carried, which increases the launch mass and the required power significantly. The receiver itself will need some structure and therefore weight as well.

1700 m/s over 300 seconds means most thrust goes against gravity drag.

1/2 GW thrust with 25% efficiency of transmitter and receiver each would need 8 GW on the ground. And I don't see how you would reach those numbers (transmitter is fine, but receiver to thrust?). Rockets and rocket-like things at low speed are not very efficient, most of the energy goes into motion of fuel.

Add all effects and you are in the range of 100+ GW.

 

[mheslep]

Yes, sorry 8 GW on the ground. Edit:
http://researchspace.csir.co.za/dspace/bitstream/10204/1014/1/Michaelis1_2006.pdf

 

[mheslep]

Add all effects and you are in the range of 100+ GW.

How so? Drop the time to 150s, the actual burn time used for the Falcoln 1st stage. That's 16 GW. You're assuming a very low receiver efficiency?

 

[mfb]

I made a conservative estimate for all the issues mentioned.

Here is a lower bound: Assume a constant exhaust velocity of v_e which we want to optimize. Longer thrusting times increase gravity drag and therefore propellant mass but reduce thrust and therefore power for the same mass, there is some optimum time T. We need a velocity change of 1700 m/s, plus gravity drag we need delta_v of $\Delta v = 1.7 km/s + gT$. The rocket equation gives us the launch mass: $M=100 t \exp{\frac{\Delta v}{v_e}}$, the difference to 100 tons we have to accelerate to v_e, which needs an energy of at least $E=50 t (\exp{\frac{\Delta v}{v_e}}-1) \cdot v_e^2$. Power is then given by energy divided by time:
$$P=\frac{E}{T}=\frac{50000kg}{T} (\exp{\frac{1.7 km/s + gT}{v_e}}-1) \cdot v_e^2$$
Optimizing this gives T=174 s, v_e = 2.14 km/s and an average power of 5.2 GW used for thrust. Applying your two 25% efficiency values, this would need 80 GW ground power. Reduce one efficiency to 20% and you are at 100 GW. The launch mass would be 490 tons, 100 tons for the second stage and 390 tons for first stage reaction mass. This is a lower bound... it overestimates gravity drag a bit as the launch profile is not vertical, but it assumes all your received energy is used to accelerate reaction mass exactly opposite to the thrust direction.

 

[mheslep]

So you completely rule out use of the atmosphere as a reaction mass, up to at least a couple dozen km? I can imagine some problems, like choosing a beam wavelength without atmospheric loss while also requring it to heat air at the receiver. But I don't know that it's impossible.

 

[mfb]

I don't rule it out, but I don't see how you would get close to 25% efficiency there.
Once the rocket moves significantly faster than the speed of sound, how do you even get the air behind the rocket - and behind something to push against?
The total mass of the air in the path of the rocket (~10 tons/m^2) is significantly below 400 tons.

 

[Monsterboy]

http://www.nbcnews.com/tech/innovation/spacex-plans-drone-ship-rocket-landing-jan-17-launch-n492471

SpaceX hopes to make history again on Jan. 17 by landing a Falcon 9 rocket on a drone ship at sea after launching a payload into orbit.

can't wait !

 

[mheslep]

...don't rule it out, but I don't see how you would get close to 25% efficiency there.

Here we go. Phipps et al derived a laser power per unit mass of 100 kW/kg to 200 kW/kg to LEO, with initial balloon lift of payload to 30-35 km, with receiver momentum efficiency as low as 3%, or up to 20 GW delivered power for a 100 ton LEO delivery. Yes, beamed propulsion appears unfeasible for a multi-ton payload as Musk (and you) indicate.

Phipps does find a cost of as little as $100/kg using beamed propulsion for ~10 kg sized payloads.

 

[mfb]

Starting at 30-35 km helps with gravity drag as you can go for a more horizontal launch profile.

 

[HyperTechno]

So as all these attempts are about saving the cost, how economical , collecting space debris to be recycled would be?
As there are lot of space debris orbiting the earth, collecting and recycling them would be a great cost cutting measure...

 

[mfb]

We don't have systems in space that could transform junk to anything useful - and we don't even have systems on Earth small and robust enough to send them to space for that purpose.
Oh, and we don't have tested systems to collect space junk either.
It could become interesting in the future, but not now. Note that lower launch costs make recycling (instead of just deorbiting) less attractive.

 

[enorbet]

ping HyperTechno - mostly about cost cutting without sacrificing safety as NASA has disastrously done a few times, yes... but also turnaround time improvement. The Shuttle was referred to as "reusable" but because of the lack of specificity and difficulties getting a sufficient launch schedule (which took serious blows, cancellations, misdirection, and many months-long repairs) never lived up to it's design imperative for rapid turnover and actual reduced cost and was severely limited in what it could accomplish (couldn't leave Earth orbit, for one) since it was originally designed for Space Station servicing, added Commercial satellites and Scientific launches and at one point lost all but Scientific which just wasn't enough turnaround to meet it's supposed goals. Going back to "vehicle-on-top" of heavy launchers should be very welcomed by all.

I hope I'm not preaching to the choir here but I think Musk's analogy is on point being "Imagine if you took a flight from New York to LA and upon arrival the plane had to be scrapped each time. How much do you suppose tickets would cost?" Presently, since the original "Golden Years" Space Station was axed by Pres. Nixon, the shuttle was a solution looking for a problem and had way too many of it's own and disposable 1st stages can't ever be practical and is perhaps the single biggest obstacle to all flights but especially manned flights.

Musk gets a labelled as simply a rich kid with delusions of grandeur, but even if that is true, the man has vision and does deliver on promises, at least so far. Personally I think this successful landing (and especially combined with the upcoming sea platform landing) is a true milestone, possibly even a for real (and needed) "course correction" so we have a chance to make all manner of Space Exploration launches viable and possible with real cost-cutting benefits without shameful Safety Management resulting in publicly horrific deaths that is always an excuse to go "back burner" or even shutdown. You may recall that Nixon scrubbed the last few Apollo Missions even though most of the hardware was already bought and paid for. We really don't need that to be a recurring disaster and this method addresses all that, with the possible exception of the whole "familiarity breeds contempt" thinking that NASA management has sometimes drifted into. Frankly, I cheered at my screen when they/we succeeded :)