Reusability of Falcon Heavy and multiple boost stages

[lklundin]

(mod note: split from SpaceX Falcon 9 FT launch - CRS 8 - SLC-40)

These videos emphasize an important point about how SpaceX manages to keep their costs as low as they do. The F9 is a pretty small rocket compared to most of the others that deliver similar payloads to orbit. SpaceX can transport their boosters and stages pretty easily since they can travel on regular roads. This is critical when your factory is in California but your launch site is in Florida. When SpaceX starts moving into much larger sized rockets, it's going to get a lot more difficult and expensive. FH is an exception since that uses the same size boosters and stages, just more of them.

Maybe SpaceX will buy a second factory for BFR in Florida or Texas and keep Hawthorne for F9 and FH.

Yes, I guess they can't just do a burn-in test with a flight from California to Florida.

On a more serious note, the mentioned Falcon Heavy seems powerful with potential for being very cost-effective, so what plans does SpaceX have for rockets with much larger stages?

 

[Grendal]

Yes, I guess they can't just do a burn-in test with a flight from California to Florida.

On a more serious note, the mentioned Falcon Heavy seems powerful with potential for being very cost-effective, so what plans does SpaceX have for rockets with much larger stages?

Elon has spoken of bigger rockets for the future. BFR (Big Effin Rocket) is its designation and will use the Raptor engine which is a Methane LOX engine. Elon has said he will outline SpaceX official plans for Mars in September. It's expected that he will introduce the BFR and the Raptor at that time. Maybe he will talk about his plans for the MCT (Mars Colonial Transporter) and all the other things we've heard about but not seen. I know SpaceX is working on a spacesuit. Though that will likely be shown during an update about CCiCap and CCDev.

Reusability is the key to all of this. If BFR will take a lot of development for reusability then it might be harder to justify if they have F9 and FH working properly. It would make BFR look silly if F9 and FH work nearly perfectly for reuse and BFR doesn't. Will BFR be designed for always landing on land? Unless they start using a cruise liner instead, I can't see using an ASDS for anything larger than F9 boosters.

Personally, I hope SpaceX develops an orbital industry and takes pieces of larger ships and fuel into orbit for assembly there. The larger ships then travel wherever is needed. The moon, asteroids, Legrange points, and even Mars is much easier to reach when you are already in orbit. It's getting out of the gravity well that has been ridiculously expensive.

 

[robertvg]

Yes, I guess they can't just do a burn-in test with a flight from California to Florida.

An on-the-road test would make for a very quick drive from FL to CA

 

[lklundin]

Reusability is the key to all of this. If BFR will take a lot of development for reusability then it might be harder to justify if they have F9 and FH working properly.

Yes.

Let's assume that FH becomes a success.

How well would it then work to extend the "asparagus staging" with two additional F9 boosters, in a Falcon 45 configuration ?

I mean, if they can get FH to work, then they should be able to launch with not just one pair, but two pairs of side boosters, symmetrically placed around the core F9 and all ignited at launch.
Per the asparagus staging concept, they could draw fuel for all 45 engines from two boosters, separate these two when empty as the first stage separation event, and then go on from there as a normal, except more energetic FH.

Although the number of separation events would be large, it would be a relatively simple evolutionary step up from a normal FH, and not really require any new parts (apart from a more advanced control of the propellant flow).

 

[glhs272]

Yes.

Let's assume that FH becomes a success.

How well would it then work to extend the "asparagus staging" with two additional F9 boosters, in a Falcon 45 configuration ?

I mean, if they can get FH to work, then they should be able to launch with not just one pair, but two pairs of side boosters, symmetrically placed around the core F9 and all ignited at launch.
Per the asparagus staging concept, they could draw fuel for all 45 engines from two boosters, separate these two when empty as the first stage separation event, and then go on from there as a normal, except more energetic FH.

Although the number of separation events would be large, it would be a relatively simple evolutionary step up from a normal FH, and not really require any new parts (apart from a more advanced control of the propellant flow).

Although I am sure the "Asparagus staging" may be technically possible, I doubt spacex will ever go there. Their launch facilities don't look to be setup to accommodate that kind of configuration. Hangers aren't tall enough, pad configuration not setup for it. FH seems to be about as big of a bite spacex can chew. Also, the Asparagus staging would likely make re-use more challenging unless spacex develops a much heavier and larger second stage (raptor based upper stage?). Otherwise those booster cores will just be flying to higher altitudes and speeds which may push the boosters beyond their melting limits during re-entry.

There aren't that many needs for a heavy lift rocket the size of Falcon Heavy expendable. Those payloads may come over time as the rocket becomes available. But for the most part the Falcon heavy is being used to stay in the re-usable zone of the Falcon series rockets. Rather than using the full performance of expending a single stick falcon, they can use Falcon Heavy to get that extra little push to the heavier payloads and still recover the boosters. Payloads that require a fully expendable falcon heavy don't seem to exist right now. That may change as rockets such as SLS come on line, for which Falcon heavy expendable may be useful for. But that will take another 5 to 10 years probably. NRO is the only one that comes to mind. NASA payloads will probably be reserved for SLS. And the commercial payloads won't exist until the rocket to carry them does (hence the 5 to 10 years).

I think we will be seeing the F9/FH flying the way it is for quite a long time now, with relatively few changes at this point. If they want more capacity, a very large single stick booster seems to be the way to go. Keep it simple with only one staging event. Stage low enough to keep the booster from melting on re-entry and make return to land possible. And carry a heavy, large, high thrust upper stage. Hopefully that upper stage will have the shielding for re-entry, for a fully reusable booster system.

 

[lklundin]

Although I am sure the "Asparagus staging" may be technically possible, I doubt spacex will ever go there. Their launch facilities don't look to be setup to accommodate that kind of configuration. Hangers aren't tall enough, pad configuration not setup for it. FH seems to be about as big of a bite spacex can chew. Also, the Asparagus staging would likely make re-use more challenging unless spacex develops a much heavier and larger second stage (raptor based upper stage?). Otherwise those booster cores will just be flying to higher altitudes and speeds which may push the boosters beyond their melting limits during re-entry.

Maybe by "Asparagus staging" we refer to two different things. I refer to it in the manner described here:

Modular rocket - Wikipedia, the free encyclopedia

- i.e. fueling (pretty much) all 27 FH engines from the two outer boosters, and then get rid of them as soon as they are empty, after which one has a normal, almost fully fueled and more energetic F9. This concept can be extended with an extra pair of boosters, for a total of 45 engines ignited on launch.

This would not require any new boosters nor lead to a taller rocket (but would make the retrieval of the more energetic core F9 more difficult).

 

[rabar10]

i.e. fueling (pretty much) all 27 FH engines from the two outer boosters, and then get rid of them as soon as they are empty, after which one has a normal, almost fully fueled and more energetic F9.

This is also known as 'crossfeed', and is highlighted in SpaceX's Falcon Heavy webpage as "Propellant Cross-Feed System".

I don't believe the first Falcon Heavy launches will support crossfeed, but it's on their to-do list for further extending performance of the 3-booster configuration.

My understanding of "asparagus staging" is extending the crossfeed principle to work among many more booster stages (5, 7, etc.). The complexity of pushing the massive volume of fuel/oxidizer between all of the stages, through quick-disconnect fittings/valves, is what prevents us from seeing this used outside of simulations i.e. Kerbal Space Program.

 

[glhs272]

Maybe by "Asparagus staging" we refer to two different things. I refer to it in the manner described here:

Modular rocket - Wikipedia, the free encyclopedia

- i.e. fueling (pretty much) all 27 FH engines from the two outer boosters, and then get rid of them as soon as they are empty, after which one has a normal, almost fully fueled and more energetic F9. This concept can be extended with an extra pair of boosters, for a total of 45 engines ignited on launch.

This would not require any new boosters nor lead to a taller rocket (but would make the retrieval of the more energetic core F9 more difficult).

That is my understanding of asparagus staging as well. My comment with respect to launch facilities is not due to the rocket being taller when vertical, but rather how the vehicle stack is integrated when horizontal in the HIF (horizontal integration facility). Instead of the Falcon Heavy three core configuration where the boosters lay on opposite sides of the core booster, which doesn't increase the overall height while horizontal. When adding the additional cores, for a total of 5 cores, once integrated the whole whole stack will be effectively up to 3 times as tall when laying horizontal (think falcon heavy laying on it's side 90 degrees from normal with one core below the center core and one core above the center core). Ends up being a lot bigger. Think how the Russian Angara launch vehicle looks when doing its roll-out. Even though they hold the rocket so the boosters are 45 degree angles from the horizon, the whole things is still taller when horizontal. I just don't think the current spacex facilities can do it (even the larger HIF at pad 39A). They could build new facilities or do strictly vertical stacking at the pad, but I doubt that will ever happen.

 

[lklundin]

My comment with respect to launch facilities is not due to the rocket being taller when vertical, but rather how the vehicle stack is integrated when horizontal in the HIF (horizontal integration facility).

OK, I see. Thanks.

I look forward to seeing what they actually end up doing.

 

[lklundin]

This is also known as 'crossfeed', and is highlighted in SpaceX's Falcon Heavy webpage as "Propellant Cross-Feed System".

I don't believe the first Falcon Heavy launches will support crossfeed, but it's on their to-do list for further extending performance of the 3-booster configuration.

My understanding of "asparagus staging" is extending the crossfeed principle to work among many more booster stages (5, 7, etc.). The complexity of pushing the massive volume of fuel/oxidizer between all of the stages, through quick-disconnect fittings/valves, is what prevents us from seeing this used outside of simulations i.e. Kerbal Space Program.

Right, thank you for clarifying that "asparagus staging" describes how the rocket stages are placed next to each other, while the crossfeeding of fuel is an additional and optional optimization.

I very much like the SpaceX development strategy, where they increase their capability by getting one thing to work, then keep that solution and then go on to figure out the next thing. So it makes sense that the F9 will be followed by a Falcon Heavy that initially will not use the crossfeed.

Even without that the FH has a high risk of not working right away.

F.ex. at the most recent Falcon 9 first stage landing, the unfolding of one of the landing legs was significantly delayed, but not enough to be a problem.

For the Falcon Heavy first separation the consequences of any asymmetry will be much worse.

If f.ex. the two side boosters do not separate at the exact same moment, the center of gravity will suddenly shift to one side, and then suddenly shift back when the other side separates. Especially with the engines of the central core still burning, I have to speculate that such a shift would strain the core booster beyond its strength. Another asymmetry could arise from the two side boosters not shutting their engines down at the same time, which again would result in non-symmetric forces on the core booster.

It will surely be exciting to watch.

 

[Grendal]

SpaceX can shut off their engines for side booster separation and do a restart on the central booster if there is any booster "separation anxiety." I'm not sure what caused the leg anomaly but timing on separation events for the rocket have gone off as planned. I believe the legs are hydraulically powered. Maybe there was a delay in the pressure build up from all three legs at once.

 

[glhs272]

SpaceX can shut off their engines for side booster separation and do a restart on the central booster if there is any booster "separation anxiety." I'm not sure what caused the leg anomaly but timing on separation events for the rocket have gone off as planned. I believe the legs are hydraulically powered. Maybe there was a delay in the pressure build up from all three legs at once.

I might be misunderstanding you, however I believe the falcon 9 cores can only restart 3 of the 9 engines once they have left the pad. I believe that is by design, as they have no need to stop/start the entire core. Generally speaking, it's not a good idea to shutdown the center core engines only to restart them later during the ascent, as they might not restart. They will just throttle back the center core shortly after take off, then throttle back up once the side boosters separate. Much like the Delta 4 heavy. If they push forward with cross-feed, then they can run all 3 cores wide open throttle until the g load nears 5Gs or if there are any max Q issues, they may have to throttle down for a little bit during that period.

 

[ggr]

SpaceX can shut off their engines for side booster separation and do a restart on the central booster if there is any booster "separation anxiety." I'm not sure what caused the leg anomaly but timing on separation events for the rocket have gone off as planned. I believe the legs are hydraulically powered. Maybe there was a delay in the pressure build up from all three legs at once.

There are four legs. They are hydraulically operated but if I was designing it they wouldn't be completely independent, since having four pumps would just increase weight and the probability of one of them not working. Instead, I'd use a couple of pumps in parallel (for redundancy) feeding a set of hydraulic lines going to all four legs. Then, what happens if there is a slight difference in the force needed to put a particular leg down is that the easier ones deploy first, then when locked, all the power goes to putting down the last one. Many airplanes with retractable landing gear show this behavior, with one wheel usually opening and closing before the other(s).

 

[glhs272]

I have no inside knowledge, however I have seen it reported that the Falcon 9 legs are pneumatic and are operated by a high pressure helium bottle.

Falcon 9 v1.1 & F9R – Rockets

 

[Grendal]

There are four legs. They are hydraulically operated but if I was designing it they wouldn't be completely independent, since having four pumps would just increase weight and the probability of one of them not working. Instead, I'd use a couple of pumps in parallel (for redundancy) feeding a set of hydraulic lines going to all four legs. Then, what happens if there is a slight difference in the force needed to put a particular leg down is that the easier ones deploy first, then when locked, all the power goes to putting down the last one. Many airplanes with retractable landing gear show this behavior, with one wheel usually opening and closing before the other(s).

That's exactly what I was picturing happening when we saw the delay in one leg. You explained it so much better. Thanks.

 

[ggr]

I have no inside knowledge, however I have seen it reported that the Falcon 9 legs are pneumatic and are operated by a high pressure helium bottle.

Falcon 9 v1.1 & F9R – Rockets

Yes, pneumatic rather than hydraulic. But I think the rest of my explanation stands, as to why some legs deploy faster/slower.