SpaceX Grasshopper and re-usable plans

[bendeezer]

The primary issue with using parachutes and splash landings on rocket boosters is that the cost of retrieval goes up as well as the time intervals for recovery, because you would have an uncontrolled landing, in a wide target area on to a surface that moves. The secondary issue with this kind of landing for reusable aircraft is that the forces involved on "landing" usually warp the airframe considerably, and a lot of time is spent on inspection and refurbishment on damaged and warped parts. The cost of fuel for a controlled safe return is actually reduces costs, and decreases the intervals between luanch-dates for a reusable craft significantly. So, it actually (profitability wise) what you definitely want to shoot for. The hurdle is wheter or not can do it safely.

[Woopert]

Hmm, just found this thread.

I was planning on starting one asking for people's opinions on taking reusability to the extent that SpaceX does.

Personally I think they take it too far... It's probably cheaper to make a new upper stage than trying to have it survive re-entry and refurbishing it. It's also safer to just make a new one, I think

Re-using the first stage seems difficult but totally do-able, don't know how effective it actually is.

Side question, why does SpaceX use RP-1 for the upper stage? Isn't LH2 more efficient? Or for SpaceX does cost > efficiency?

[SargeRho]

RP1 is easier and safer to handle than LH2. Also you can build smaller (read: cheaper) rockets with RP1 as it's much denser than Hydrogen. They use RP1 for both the first and 2nd stage, because the two stages use the same engines, exept slightly modified for vacuum operation on the upper stage.

They plan to switch from RP1 to LNG, aka Methane.

[sojourner]

They plan to switch from RP1 to LNG, aka Methane.

This remains to be seen. I think Falcon 9 will continue to use RP-1. The methane engine they are developing is much too large for Falcon 9 and will most likely be used on SpaceX's BFR.

[DeepSpaceDutch]

Well things are starting to come together Elon just posted this picture of the landing legs added to the Falcon 9 for next months flight to the ISS;

Looks very Kerbal to me

[DeepSpaceDutch]

Personally I think they take it too far... It's probably cheaper to make a new upper stage than trying to have it survive re-entry and refurbishing it. It's also safer to just make a new one, I think

According to Mr. Musk the math checks out, I tend to believe Mr. Musk's statements

[bigdad84]

4 landing legs are set and ready to go!

[Superluminaut]

Does the f9 use a special tech to position the fuel for reignition on the recoverable stage out do they use the standard method?

[MaverickSawyer]

The stage assumes a tail-first orientation, so air drag is more than enough to settle the fuel on final landing.

For the separation burn, they probably use some sort of ullage thruster. Maybe a pair of Dracos...

[sojourner]

The first stage has cold gas thrusters at the top of the stage. No Dracos.

Not sure what you mean by "separation burn". When the second stage separates gravity pretty much does the work for the second or two before the second stage engine fires.

Edited February 26, 2014 by sojourner

[bigdad84]

Bit of a thread revival here.... But we're 4 days away from anything propulsive landing over water, but with landing legs this time.

Also just had a successful static fire test! That rocket looks so sleek and sexy!

Edited March 12, 2014 by bigdad84

[sgt_flyer]

Does the f9 use a special tech to position the fuel for reignition on the recoverable stage out do they use the standard method?

I think they also worked on a new control system, to prevent the stage from spinning during the freefall part of the descent. (That's what prevented the previous return over water from reigniting it's engines prior to the landing burn, because the fuel had centrifuged inside the tank due to the spinning)

[EuroSnob]

Some more exciting pictures, showing the F9/Dragon and legs: http://www.spacex.com/news/2014/03/11/upcoming-mission-falcon-9-and-dragon-launching-space-station

[sojourner]

I think they also worked on a new control system, to prevent the stage from spinning during the freefall part of the descent. (That's what prevented the previous return over water from reigniting it's engines prior to the landing burn, because the fuel had centrifuged inside the tank due to the spinning)

The legs are supposed to provide spin stabilization, acting like fins.

[Camacha]

Like fins, or by extending and thus slowing rotation down (angular momentum and such)? For the use of fins you need air, I would say.

[MaverickSawyer]

Both. The "ballerina effect" and the increased drag along the roll axis will help keep the roll rate to a level that the rocket/attitude control system can tolerate.

[sojourner]

Like fins, or by extending and thus slowing rotation down (angular momentum and such)? For the use of fins you need air, I would say.

The spin didn't become a problem until right before the final landing burn on the previous attempt. Plenty of air that low in the atmosphere. The legs don't deploy until the final landing burn of the engine.

[CalculusWarrior]

This is exciting! In the upcoming launch, will the 1st stage slow down to landing-ish speeds before dropping into the water, or will they just test fire the engines and let it crash into the ocean?

[sojourner]

They are going to try and soft land it in the water. It's basically going to do everything it needs to do to successfully land on land, but will be over the ocean when it does it.

[Brotoro]

Is it going to come back up range to somewhere near the launch site, or just try to soft land in the water far down range?

[astropapi1]

And then, are they gonna simply let it drift away on the ocean?

[Ralathon]

And then, are they gonna simply let it drift away on the ocean?

They're going to try and recover it to get moar data. But I doubt they're going to reuse the stage. Salt water + delicate rocket engines is a bad mix. Maybe they'll be able to salvage some bits, but most will go into the garbage bin once the engineers are done picking it apart.

[sojourner]

It's unclear from everything I've read if they are actually going to bring it back close to the coast for the water landing attempt. Hopefully so. Regardless, if things go well and the stage is recovered, after teh engineers get done with examining it, I am guessing it will go on display somewhere at the Hawthorne plant.

[DonLorenzo]

I'm guessing they're not bringing it back. Doing so would incur a big dV hit, and they're doing this as an 'extra' on a regular paid launch. So I'm guessing it's not got the dV headroom to do so (since otherwise why would the customer not use a lighter launcher)

[sgt_flyer]

well, the CRS-3 will be launched by the falcon 1.1, which has a 13tons payload to LEO - the dragon capsule is almost half this weight (with payload), so i think they'll have plenty of spare fuel for their test (after all, after the initial turnaround, the descent is 'free' until landing )