SpaceX

[chickensevil]

Has Elon or anyone mentioned why they aren't using parachutes to help slow down the first stage during recovery?

I don't think so by them but it has been discussed by others and it really wouldn't work. Issue one, added weight. The chutes take up both space and weight on the rocket meaning a lower payload. Issue 2: the speed that the craft is moving EVEN AFTER its initial burn coming back into the thick part of the atmosphere would shred through the chutes and male them useless.

I know what you are think the capsules have all used chutes why not for this? The difference here is that the capsules have a rather large area under them that have been heat shielded and then they push the craft through a very shallow angle into the atmosphere causing it to have a lot more time and resistance to slow down. Instead these rockets are not shielded (the the extent that would allow this) and are taking a very steep angle straight down. This causes them to break through the atmosphere with minimal slowing.

Finally you are overestimating how costly the fuel is to the rocket payload. Consider that from launch to separation you have a full 2 minutes 30 seconds of full 9 engine burn. How long on the return are they relighting the first stage? 15-20 seconds? And we are talking just one single engine. So that is assuming 30 seconds 1/9th of 1/8th the fuel needed to slow the first stage. It is really not that much.

It is a common line of thinking but it just doesn't work in this case.

 

[rabar10]

Has Elon or anyone mentioned why they aren't using parachutes to help slow down the first stage during recovery?

Just to add to the other replies -- they tried parachutes on the first few Falcon 9 launches in 2008-2009. The initial idea was to add some thermal protection systems (heat shielding) to the first stage and control its orientation as it fell, then pop the chutes to splashdown in the ocean and recover. They never got it to survive atmospheric re-entry though. This was all before they started doing the retro-propulsion landing attempts.

 

[chickensevil]

Just to add to the other replies -- they tried parachutes on the first few Falcon 9 launches in 2008-2009. The initial idea was to add some thermal protection systems (heat shielding) to the first stage and control its orientation as it fell, then pop the chutes to splashdown in the ocean and recover. They never got it to survive atmospheric re-entry though. This was all before they started doing the retro-propulsion landing attempts.

Oh well, there you go! See I knew other companies had tried the whole reusability thing previously, and I had heard that was how other companies had attempted to solve it... failed... and gave up. I didn't realize that SpaceX had also at first attempted to go that route as well. So thanks for the background

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Probably doesn't need to be optimized for atmospheric operation, because by the time it's doing it's thing much of the mass of the spacecraft will be gone (payload and fuel).

I wanted to pry you, to see if you had more details/thoughts on this subject. Because I think current line of thinking is for them to throw a super draco engine or something similar onto the rocket in order to allow it to have some kind of thrust capability once it comes back down. It is true that it won't need much power given its lack of a payload and almost empty fuel tanks. But I think the issue with adding another engine (or two) onto this, even small ones, will eat into the weight of the rocket and reduce their payload capacity.

Is there something I am missing from the vacuum engine? is it able to actually work at all in the atmosphere? My understanding was: no.

 

[Doug_G]

Is there something I am missing from the vacuum engine? is it able to actually work at all in the atmosphere? My understanding was: no.

I'm pretty sure the difference between the atmospheric and vacuum engines is just the shape of the cone. It's optimized differently for the different pressure regime. The fuel/oxidizer mixture in a rocket does not need anything from the atmosphere in order to burn.

 

[rabar10]

Is there something I am missing from the vacuum engine? is it able to actually work at all in the atmosphere? My understanding was: no.

Doug_G is right: rocket engines by definition carry both fuel and oxidizer with them, unlike jets/ramjets/scramjets etc. which use oxygen from the atmosphere. So the combustion part works the same in space or on the ground. But the nozzle is different on the second-stage MVac for efficiency reasons.

The stage 2 nozzle has a larger expansion ratio, i.e. ratio of engine throat diameter (narrowest part) to nozzle tip diameter (widest part). That's because at higher altitudes, the atmosphere isn't pushing back against the rocket exhaust with the same pressure as on the ground, so the exhaust expands sideways. This is why the exhaust plume from the first stage grows sideways as the rocket rises up through the atmosphere.

But sideways expansion doesn't do any useful work to push the rocket up -- so a bigger/longer nozzle works to harness more of the energy to push upwards instead of just "out". Good for the second stage engine that operates in/near space. But all that extra nozzle material would be wasted weight on the first stage engines.

Back to eventual goal of second-stage return and landing -- SpaceX would likely use different engines than the MVac to do the final landing burn, simply because that engine is too powerful and can't be turned down or throttled deeply enough. So yeah, something more like the SuperDracos.

 

[c041v]

Part of me wonders if they could create an adjsutable nozzle, similar to the Convergent Exhuast Nozzle Control system on the F15 Eagle's P100's. I heard that they had to be replaced fairly often, and were controlled by bleed air off the compressor, but it would be cool to "throttle" the engine by adjusting the nozzle diameter/shape.

Also not sure how much hotter RP1/LOX burns than than JP1...

 

[rabar10]

Part of me wonders if they could create an adjsutable nozzle...

Altitude compensating nozzle - Wikipedia, the free encyclopedia
Lots of ideas listed there, including:

Expanding nozzle - basically sliding a nozzle extension down over the smaller nozzle as the rocket gains altitude
Plug nozzle - think of a garden hose sprayer, adjust the central plug near the exit to adjust the shape of the exhaust
Aerospike engine - a radically different-shaped rocket exhaust structure, either linear or toroidal, with no moving parts

But to date very few of these have made it into production or practical use. For multi-stage rockets a traditional can be optimized for the operating altitudes of that stage.

 

[chickensevil]

Very informative information, thank you. I was thinking almost exactly the opposite, since if you look at something like... Saturn V... the first stage engines are significantly bigger on the nozzles than the second and third stage... although that could just be because of a change in fuel type as well? Since those upper stages burned hydrogen instead of JP-1.

In any case, what you are saying makes sense to me. So in reality the second stage engine would perform VERY WELL as a lander... to the point where it would perform too well? As in... WAAAAY too much thrust even throttled to 70%? Why couldn't they just use the same technique as the first stage by just firing it at the precise moment that would allow it to hit exactly 0 velocity at 0 altitude?

Another question about the second stage landing, are they just going to stick legs on it way up the side of the rocket? Would look kinda... funny... Although give it's much lower weight profile maybe they could be much smaller and therefore tuck in underneath the interstage piece? From the pictures I have seen it looks like there would be room inside, maybe?

If they wanted to stick some tiny engines in there, they might also have room for that as well, would probably need 4 though to get the proper even spread, which seems like a huge weight concern... hrmmmm I really have not clue how they plan to solve that one! Doesn't seem as simple as "just stick legs on it".

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And this is where I think Firefly is making an interesting push into the space arena in that they are intending to use an Aerospike engine. We will find out how well it fares over the traditional design.

 

[aronth5]

SpaceX Sets November, January Dates for Launch Abort Tests of Crew-capable Dragon

http://www.spacenews.com/article/launch-report/41515spacex-sets-november-january-dates-for-launch-abort-tests-of-crew-capable

 

[woof]

I thought I recalled that one of the reasons to not use 'chutes was because with the thinner atmo on Mars they wouldn't be effective, so learning how to do a thruster landing was to enable the ability to land on Earth, Moon, and Mars. I did a search and couldn't find anything that validates this recollection however. This one comes close: (from 2011, a long time ago in SpaceX history!) SpaceXs Future Spaceship Forgets Parachute : Discovery News

 

[Doug_G]

Pretty sure it was all about being able to land accurately near the launch site, so you can recycle the vehicle quickly. But I do think whenever there's a close choice between two technologies, and one is more suited to Mars than the other, they go with the Mars option.

 

[Cosmacelf]

Got it, yes I do remember now that landing on Mars was an important reason for no parachutes...

 

[markwj]

I remember reading that for the crew capsule (Dragon v2) they intend to have parachutes as a backup. The idea is that as the capsule descends, the rockets are test fired. If that fails, then parachutes are deployed.

 

[chickensevil]

SpaceX Sets November, January Dates for Launch Abort Tests of Crew-capable Dragon

SpaceX Sets November, January Dates for Launch Abort Tests of Crew-capable Dragon | SpaceNews.com

Your link didn't get processed correctly (at least on my end), So I fixed it for you.

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I thought I recalled that one of the reasons to not use 'chutes was because with the thinner atmo on Mars they wouldn't be effective, so learning how to do a thruster landing was to enable the ability to land on Earth, Moon, and Mars. I did a search and couldn't find anything that validates this recollection however. This one comes close: (from 2011, a long time ago in SpaceX history!) SpaceXs Future Spaceship Forgets Parachute : Discovery News

So continuing this line of thinking, one of my friends has this whole entire thought process that everything Elon is doing right now is because it has some kind of direct application with Mars.

Battery Backup Storage + Solar -> Pretty much the best thing they can hope for power on Mars
Super Energy Dense batteries that are also lightweight -> How much space is taken up in a spaceship to power all the computer systems and such?
Electric Cars -> You think we would use gas cars on Mars? HAHAHAHA NOPE!
Hyperloop -> Would work as long distance travel in a low atmospheric planet EVEN BETTER!

The list goes on... It was an interesting thought, and one that I couldn't exactly disagree with. Rockets landing under their own power also makes sense from that perspective as well.

 

[ecarfan]

@chickensevil, I have thought that for some time now. It seems clear that Elon's primary goal in life is developing technologies that enable permanent human settlement on Mars. That is why he will decrease his involvement in Tesla a few years from now, and as a TSLA owner I'm fine with that. He needs to focus his energies on SpaceX.

I am confident that within 20 years there will be a permanent base on Mars, and it won't be established by NASA. In 10 years Tesla may well be the most valuable car company in the world, and Elon can use his stock profits to fund missions to Mars.

I am glad I am likely to live long enough to see that happen. When I was growing up I read Asimov, Clarke, Bradbury, and others, and I have been disappointed that humans have not made more progress in manned space exploration.

Now I read Kim Stanley Robinson and Robert Zubrin.

So continuing this line of thinking, one of my friends has this whole entire thought process that everything Elon is doing right now is because it has some kind of direct application with Mars.

 

[ggies07]

So continuing this line of thinking, one of my friends has this whole entire thought process that everything Elon is doing right now is because it has some kind of direct application with Mars.

Battery Backup Storage + Solar -> Pretty much the best thing they can hope for power on Mars
Super Energy Dense batteries that are also lightweight -> How much space is taken up in a spaceship to power all the computer systems and such?
Electric Cars -> You think we would use gas cars on Mars? HAHAHAHA NOPE!
Hyperloop -> Would work as long distance travel in a low atmospheric planet EVEN BETTER!

The list goes on... It was an interesting thought, and one that I couldn't exactly disagree with. Rockets landing under their own power also makes sense from that perspective as well.

Interesting....never put that list together, but I like it.

 

[Mario Kadastik]

Was reading the comments here:

Spaceflight Now United Launch Alliance announces leadership change

And one perked my interest:
Slavi Mirtchev · Gaithersburg, MarylandThe Falcon Heavy could've flown in 2014 but they want to try to get reusability working. Why waste 3 cores on a demo flight that no one's paying for?




I know that SpaceX delayed the Falcon Heavy demo flight because they had such a busy schedule that producing three spare cores just for the demo flight wasn't a good plan so they produce them on the side slowly and expected the launch to happen in 2015. Now that comment put it even into a better context that if indeed they target the FH flight after they have demonstrated reusability they'd have three spare cores that they recover and could fly either as another FH or as three separate F9R flights at extremely low cost to recoup some of the demo flight losses (a flight that I no doubt expect them to have a customer flying on at a substantial discount, but still making up some of the cost).

 

[palmer_md]

Now that comment put it even into a better context that if indeed they target the FH flight after they have demonstrated reusability they'd have three spare cores that they recover and could fly either as another FH or as three separate F9R flights at extremely low cost to recoup some of the demo flight losses (a flight that I no doubt expect them to have a customer flying on at a substantial discount, but still making up some of the cost).

Or the heavy demo flight is made up of three previously recovered cores, and commercial flights still all get new units...for now.

 

[chickensevil]

Or the heavy demo flight is made up of three previously recovered cores, and commercial flights still all get new units...for now.

I think this would be more likely, thereby making the test flight almost free... since three stage 1 cores have to be extremely expensive!

 

[ItsNotAboutTheMoney]

Or the heavy demo flight is made up of three previously recovered cores, and commercial flights still all get new units...for now.

His first part suggested that.

I can imagine them running cheap Falcon heavy flights that can hit orbit on 18 engines...