SpaceX Grasshopper and re-usable plans

[jfull]

So, I've been looking up lots of SpaceX stuff and I've come across their plans to make all of their rockets reusable by fitting the boosters with landing legs and literaly flying them back to the launch pad.

What I'm wondering is whether or not this is really effective. Yes, it means that the boosters are reusable, but it also means you have to separate them while they have a significant amount of fuel left so that they can land. This would reduce the payload you could lift with the rocket.

Also, if something goes wrong, you then have a partially fueled stage falling back to the launch site at high speed.

Wouldn't it be easier to use parachutes at some point during this process? That way the engines would only need to be used to to set the trajectory and for the final touchdown. It might mean that it wouldn't be able to land as accurately, but it wouldn't require as much fuel.

[sal_vager]

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[relin]

If the engine failed mid-landing, the engine wouldn't be falling back to the launch site (gravity turn, rotation of the earth, etc.) but to the open earth surrounding it. That's not to say it couldn't land in an area that could kill someone, but I'd wager is around the probability of a plane landing in the same kind of place: not good enough to worry about. And I don't see how NASA would allow this sort of thing without a purely mechanical redundancy like chutes, regardless of how reliable it is.

[maccollo]

The main issue I see with the way spaceX is doing it is not that they have to land the rocket with powered descent, but that they have to carry enough fuel to accelerate back towards the launch pad.

I don't have exact figures but at the point of first stage separation the falcon 9 is moving away from the launch pad at at least 2 km/s. So they have to stop that momentum, accelerator back to the launchpad and then land.

[Scotius]

Simplest solution would be to buy or lease a nice, wide swath of land on the other side of Atlantic. First stage would do its job, decouple, let atmosphere slow it down considerably, and then perform a powered landing. Then it could be loaded onto a cargo freighter and delivered back home.

[Nibb31]

There is a payload penalty. The Falcon9R will have a payload of 7 tons to LEO instead of 13 tons for Falcon 9-1.1, which makes it useless for the GEO comsat launch market, but it should still be able to launch a Dragon to the ISS.

Whether it's economical in the long run or profitable has yet to be seen.

Edited January 30, 2014 by Nibb31

[Nibb31]

Simplest solution would be to buy or lease a nice, wide swath of land on the other side of Atlantic. First stage would do its job, decouple, let atmosphere slow it down considerably, and then perform a powered landing. Then it could be loaded onto a cargo freighter and delivered back home.

No, it would need to burn way more fuel to cross the Atlantic than to go back to KSC. A better bet would be a launch from Texas and a landing in Florida, but even then it would need an extra boost or else it would land in the middle of the Gulf of Mexico. On a conventional launch, the first stage only splashes down 2 or 300 km east of the launch site.

[G'th]

Wouldn't be simpler, ultimately cheaper, and more practical to just attach large parachutes to the boosters? Perhaps using some kind of minimal guidance system to rotate the booster as it falls so that the parachutes can open without either tearing themselves or the booster itself apart? I can't imagine parachutes (even ones strong enough to bring down a booster) would cut into your payload that much.

Seems to me a powered descent is overly complicated for what they want to do. Like using a fork lift to change a light bulb. (not an accurate analogy but you get my point)

[maccollo]

Wouldn't be simpler' date=' ultimately cheaper, and more practical to just attach large parachutes to the boosters? Perhaps using some kind of minimal guidance system to rotate the booster as it falls so that the parachutes can open without either tearing themselves or the booster itself apart? I can't imagine parachutes (even ones strong enough to bring down a booster) would cut into your payload that much.

Seems to me a powered descent is overly complicated for what they want to do. Like using a fork lift to change a light bulb. (not an accurate analogy but you get my point)[/quote']

I think the ultimate goal of space X is to make their rockets "rapidly reusable". They want to basically land everything back at the launch site, quickly reassemble, refuel and then go.

[Psycix]

IIRC they lose about 30% payload capacity.

Fuel is only 0,2% of rocket cost.

Reusing the rocket lowers cost by up to 10 times.

If they can pull it off, it will be effective.

Parachutes are different in real life. The parachutes on the space shuttle SRB's weigh several tonnes. Since landing the rocket engines in salt water is a bad idea, they need to gently touch down the stage down on land. THe parachutes would have to be gigantic.

Bringing several tonnes of fuel instead is cheaper, lighter, more effective and more reliable, allowing for a more precise and softer landing.

Edited January 30, 2014 by Psycix

[G'th]

I think the ultimate goal of space X is to make their rockets "rapidly reusable". They want to basically land everything back at the launch site, quickly reassemble, refuel and then go.

Hmm, this is true. Presuming it works then presumably the payload penalty would be irrelevant.

[Nibb31]

Wouldn't be simpler' date=' ultimately cheaper, and more practical to just attach large parachutes to the boosters? Perhaps using some kind of minimal guidance system to rotate the booster as it falls so that the parachutes can open without either tearing themselves or the booster itself apart? I can't imagine parachutes (even ones strong enough to bring down a booster) would cut into your payload that much.

Seems to me a powered descent is overly complicated for what they want to do. Like using a fork lift to change a light bulb. (not an accurate analogy but you get my point)[/quote']

Reusing a higly complex rocket engine after dunking it in seawater is hard. The engine nozzle and the tank structure are also light and fragile, so you would probably damage the stage beyond reusability anyway.

[Nibb31]

Sorry for the repost:

Reusability doesn't necessarily reduce launch costs. The Shuttle is a good illustration. There are many other factors that need to be taken into account, and reducing the cost of the hardware is only a small part of the problem. There is a rule of thumb in the space industry called the rule of fifths: "One fifth of the budget for the satellite bus, a fifth for the rocket, a fifth for ground systems, a fifth for the payload, and the rest for various systems work (e.g. integration)."

The biggest cost isn't propellant or even hardware. It's manpower. There are thousands of technicians and engineers involved in a space project, many of which are typically high-pay-grade professionals, but there are also administrative costs, HR, training, maintenance, facilities, energy, transport, etc... Reusing part of the hardware only saves you some of the manufacturing wages, but you still have to pay for all the infrastructure and other fixed costs.

Ultimately, if reusing the first stage only impacts the fifth of the budget that is allocated to the rocket, then in that fifth, you still have the cost of refurbishing, testing, transport, refueling, etc... and the upper stage isn't reusable yet, so end customers are potentially looking at a rough estimate of much less than 20% savings on their project compared to an expendable launch vehicle. You're looking at a 10% saving on the total project, at best.

Also remember that the reusable Falcon 9R will have a reduced payload. It will be competing with the medium-lift Soyuz market, not the heavy GEO comsat market. And remember, some of the fundamental systems haven't been proven yet. Nobody knows yet if a Merlin engine can actually restart facing a supersonic airflow, or if the lightweight tank structure can resist the stress of reentry and landing without damage. This is stuff that has hardly been researched, let alone tested, and yet the whole concept relies on it working. There is still a long road before anyone can assess the idea as feasible.

There are other ways of making stuff cheap. For example, mass production of disposable items. That is the route that Arianespace is following with the Ariane 6: 4 near-identical SRBs per rocket for 12 launches per year means that the factory has to churn out nearly 50 solid booster cores per year. In space terms, that's mass production, and has the potential to massively reduce costs.

SpaceX is also going this way, with a facility that is designed to build 400 Merlin engines per year, the equivalent of 40 falcon 9s. But that pretty much flies in the way of their reusability plans, because once SpaceX starts reusing all those Merlins, their production facility has to slow down and loses its competitive advantage.

Add to the fact that the commercial launch market isn't expanding at a huge rate. The comsat market is reaching saturation while land-based networks are becoming more pervasive. The institutional market is under a lot of pressure too. And new markets will need more than a 20% discount to become viable. In fact, there isn't really much demand for a higher launch rate right now.

So, you see, there's very fine balance to be found in the industry, and I applaud SpaceX for trying something new. But this is an industry where technical achievements, no matter how impressive they are from an engineering standpoint, don't always become an industrial success. The success of SpaceX relies on much more than just bringing their rocket back to the launch pad.

Edited January 30, 2014 by Nibb31

[Motokid600]

I just can't for the life of me picture how the first stage returns to the launch pad. Once it separates the stage has to turn around, kill its forward velocity, then accelerate to the same velocity in the opposite direction? That just seems so.. improbable.

The second stage make more sense to me. It orbits the planet once, retro burn, reentry, powered landing. But turning a rocket around and flying back where it came from? I cant imagine it. Granted the stage will be much lighter... But still.

[Nibb31]

I just can't for the life of me picture how the first stage returns to the launch pad. Once it separates the stage has to turn around, kill its forward velocity, then accelerate to the same velocity in the opposite direction? That just seems so.. improbable.

The second stage make more sense to me. It orbits the planet once, retro burn, reentry, powered landing. But turning a rocket around and flying back where it came from? I cant imagine it. Granted the stage will be much lighter... But still.

That's what it does. It flies a more vertical profile than a conventional launch, which causes some of the payload capacity penalty, but minimizes the horizontal delta-v to turn around. Then it separates with some fuel left in the tank, and performs a "kick back manoeuver". The delta-v required to turn around is much lower when you are going the slowest, which is when you are at apogee.

Reusing the upper stage is orders of magnitude more complicated, and only a notional concept right now. The upper stage goes much faster and requires a heavy TPS, which also eats into the payload capacity. The mass penalty of the extra fuel and landing gear is more severe on the upper stage, and on a normal profile it's suborbital, so it would also need an extra boost to make a full orbit.

Edited January 30, 2014 by Nibb31

[tavert]

And remember, some of the fundamental systems haven't been proven yet. Nobody knows yet if a Merlin engine can actually restart facing a supersonic airflow, or if the lightweight tank structure can resist the stress of reentry and landing without damage. This is stuff that has hardly been researched, let alone tested, and yet the whole concept relies on it working. There is still a long road before anyone can assess the idea as feasible.

Interesting post, and I don't know when you originally wrote it, but this piece in particular is at least partly rectified now. The CASSIOPE test demonstrated supersonic retro burn, and survival of the first stage down to a few meters above the ocean. There's a grainy photo floating around taken presumably from some kind of aircraft close to the intended splashdown point, where everything looks surprisingly intact. I'm not sure if the photo was taken before or after the centrifuging flameout problem though. There's still lots of work for them to do, and you're right that reusing the first stage won't immediately be a silver bullet, but what they've already accomplished is extremely impressive.

[sgt_flyer]

There's a new planned test of the falcon 9R first stage return capabilities the 22 february - during the Dragon CRS3 mission.

(They only plan to land it in water and retrieve it for analysis at the moment)

The first time they tried, after 'braking' the stage post separation, the stage ended up rolling too much for their control system to handle, during the controlled descent, centrifuging the fuel inside the tanks - and they could not reuse the engine to cushion the water landing. (As the fuel was not settled in, no fuel for the turbopumps) - they only retrieved debris this time.

[Nibb31]

Interesting post, and I don't know when you originally wrote it, but this piece in particular is at least partly rectified now. The CASSIOPE test demonstrated supersonic retro burn, and survival of the first stage down to a few meters above the ocean. There's a grainy photo floating around taken presumably from some kind of aircraft close to the intended splashdown point, where everything looks surprisingly intact. I'm not sure if the photo was taken before or after the centrifuging flameout problem though. There's still lots of work for them to do, and you're right that reusing the first stage won't immediately be a silver bullet, but what they've already accomplished is extremely impressive.

Yes, I missed that. The Cassiope first stage did successfully retro-fire the Merlins in the supersonic airflow. But I don't think it splashed down intact. My understanding is that the engines flamed out way before due to the centrifugation. Not bad for a first attempt though, and nothing that can't be fixed.

[sojourner]

The biggest cost isn't propellant or even hardware. It's manpower. There are thousands of technicians and engineers involved in a space project, many of which are typically high-pay-grade professionals, but there are also administrative costs, HR, training, maintenance, facilities, energy, transport, etc... Reusing part of the hardware only saves you some of the manufacturing wages, but you still have to pay for all the infrastructure and other fixed costs.

Ultimately, if reusing the first stage only impacts the fifth of the budget that is allocated to the rocket, then in that fifth, you still have the cost of refurbishing, testing, transport, refueling, etc... and the upper stage isn't reusable yet, so end customers are potentially looking at a rough estimate of much less than 20% savings on their project compared to an expendable launch vehicle. You're looking at a 10% saving on the total project, at best.

Your numbers here are way off. SpaceX from the start has designed Falcon 9 to minimize the "standing army" involved in launch operations. Your "rule of fifths" has also counted the payload twice (satellite bus and payload) when payload is actually separate from launch costs. So really, SpaceX is dealing with a rule of thirds. manpower/fuel/hardware, in which fuel is negligible. So any significant reuse of hardware, assuming that the hardware doesn't have to be nearly rebuilt each time (like the STS) will result in very nice reductions in cost to SpaceX/the customer.

The whole design ethos of SpaceX has been "cost effective" as opposed to "bleeding edge". If they overcome the few remaining hurdles to first stage recovery they'll be in good shape to lower launch costs.

[tavert]

But I don't think it splashed down intact.

It was no longer intact after it hit the water. It's hard to tell what condition everything was in immediately prior to hitting the water from just telemetry and a grainy photo, but from what they've shared with the public it sounds encouraging.

[TheSandDuna]

I can see why people dislike this method, however I think it is absolutely brilliant by SpaceX. First of all the entire point of a first stage is to get the payload UP, and overcome gravity, so the boosters that would land back at the launch site (or at some other location) would be traveling mostly vertically and only need enough fuel to combat descent. Which brings up another point that the landing site could be separate from the launch site, a predetermined location that would require less fuel to land at. All the booster would have to do is counter its own weight and minor horizontal forces. So by saving a small percentage of the takeoff fuel from the first stage in order to save a booster for multiple flights, this is a pure genius move. The rest of the rocket can be designed knowing that there is some extra weight for this purpose.

[RuBisCO]

I think it ballzy as heck, I would not be so daring, but if spaceX gets it to work it will be incredible!

Fly back reusably as traditionally proposed used wings to glide a booster back, such as the early fully reusable shuttle proposal of a booster shuttle and and orbital shuttle, the booster shuttle would glide back and land on a runway. SpaceX idea forgoes the need to wings (or a runway) hypothetially it could land right back at it luanch tower!

Edited January 31, 2014 by RuBisCO

[magnemoe]

Your numbers here are way off. SpaceX from the start has designed Falcon 9 to minimize the "standing army" involved in launch operations. Your "rule of fifths" has also counted the payload twice (satellite bus and payload) when payload is actually separate from launch costs. So really, SpaceX is dealing with a rule of thirds. manpower/fuel/hardware, in which fuel is negligible. So any significant reuse of hardware, assuming that the hardware doesn't have to be nearly rebuilt each time (like the STS) will result in very nice reductions in cost to SpaceX/the customer.

The whole design ethos of SpaceX has been "cost effective" as opposed to "bleeding edge". If they overcome the few remaining hurdles to first stage recovery they'll be in good shape to lower launch costs.

Payload is the cargo the customer pays for. yes it its an dragon pod that is basically another stage but accounted differently.

Still the mass production statement stands, spacex will do both reuseable and standard missions, for falcon heavy they probably want to reuse the two boosters as fast as possible as they are dropped earlier and closer to pad. Guess they will also retire engines by using them in expendable stages as needed and before they starts getting unreliable. An engine used 10 times is more likely to work next time then one new.

[Nibb31]

Your numbers here are way off. SpaceX from the start has designed Falcon 9 to minimize the "standing army" involved in launch operations. Your "rule of fifths" has also counted the payload twice (satellite bus and payload) when payload is actually separate from launch costs.

The payload and satellite bus are part of the total project cost. I'm not talking about just the launch cost, I'm talking about what it costs a customer to get a satellite in orbit to do a specific job. Together they count as two fifths, because the operational payload (instruments, transponders, whatever) is usually expensive, but of course, it's only a quick estimation of how much a space program costs. My point is that savings on the launch vehicle won't impact payload, ground station, transport, testing, infrastructure, etc... and therefore only has a marginal impact on the total program cost for the customer. And if they reuse a stage 10 times, that doesn't make it cost ten times less, because there will be overhead.

We are talking about commercial or institutional satellites launches here. NASA doesn't want reused hardware for ISS Dragon trips. They will be free to reuse the hardware from NASA launches, but only for commercial launches, if they can actually find customers for 7t launches to LEO.

So really, SpaceX is dealing with a rule of thirds. manpower/fuel/hardware, in which fuel is negligible. So any significant reuse of hardware, assuming that the hardware doesn't have to be nearly rebuilt each time (like the STS) will result in very nice reductions in cost to SpaceX/the customer.

It's a misconception that STS was "rebuilt each time". The engines were removed and rotated, which limited the downtime, systems were checked, fluids were purged... Most of the parts that were taken out were actually rotated between the orbiters to keep up with the schedule. The Shuttles weren't totally ripped apart between each flight, but it was a very complex machine.

SpaceX is aiming for rapid turnaround, but there are only so many corners you can cut. They are still going to have to perform extensive verification of the stages before stacking them again. They are still going to have to purge fluid circuits and test the engines. The tanks especially are going to need intensive verification, because they are going to be subject to all sorts of loads and they are usualy made of thin sheets of metal. Any cracks or bends, and the structure can fail during the next launch.

It certainly won't be land-refuel-launch without any tests or verification, and there will be quite some manpower involved in the refurbishing work.

The whole design ethos of SpaceX has been "cost effective" as opposed to "bleeding edge". If they overcome the few remaining hurdles to first stage recovery they'll be in good shape to lower launch costs.

I disagree. They are trying lots of stuff that hasn't been tried before. There is lots of innovation going on in that company. The idea is that some ideas might fail, others might stick technically and economically. SpaceX is about as bleeding edge as it gets...

Edited January 31, 2014 by Nibb31

[Kryten]

Your numbers here are way off. SpaceX from the start has designed Falcon 9 to minimize the "standing army" involved in launch operations. Your "rule of fifths" has also counted the payload twice (satellite bus and payload) when payload is actually separate from launch costs. So really, SpaceX is dealing with a rule of thirds. manpower/fuel/hardware, in which fuel is negligible. So any significant reuse of hardware, assuming that the hardware doesn't have to be nearly rebuilt each time (like the STS) will result in very nice reductions in cost to SpaceX/the customer.

You've misinterpreted that statement quite badly, but that's to be expected given it's been taken out of it's original context. Here's the first version of it here;

Satellite operators operate (very roughly) on the 'rule of fifths'; a fifth of the budget for the satellite bus, a fifth for the rocket, a fifth for ground systems, a fifth for the payload, and the rest for various systems work (e.g. integration). If you somehow reduce launch costs to nothing at all, you've introduced the world to the clearly revolutionary potential of four-fifths current cost spaceflight.

Which I pretty much just paraphrased from this post;

In the National Security arena at least, the traditional "rule of thumb" is that launch cost represents about a fifth of the cost of a mission, the other fifths being spacecraft bus, payload (in this context "payload" means the instruments/gadgets that are carried by the spacecraft bus, and it is usually a bit more than 1/5 of the total cost), the ground system (usually a bit more then 1/5) and the systems engineering, oversight, etc. (usually a bit less than 1/5). The ratio for science missions is a bit different, but launch is usually about 25% of the total missions cost.

which was incidentally made by this fellow. Given his experience in the area, it's pretty reasonable to assume he knows what he's talking about.