Flyback boosters

[KerikBalm]

So, I tried to make a 100% recoverable two stage rocket...

When I say 100% recoverable, I mean that it lands back at KSC for 100% recovery, not across the ocean...

IIRC, SSTO rockets get payload fractions of about 10%, I thought that maybe I could improve this with a two stage design. The 2nd stage of course needs some fuel to reverse its direction and flyback

I got it working, but my results were dissappointing... I only got about a 12.3% payload fraction, and about 490 funds per ton... which is not very good at all. Barely better than the best disposable launchers, barely better than rocket only SSTOs... and that's using 4x panthers in afterburning mode to help with the launch. Later today, I want to get rid of airbreathing altogether to make it more comparable to a pure rocket SSTO. I don't think this staged flyback approach will ever pay off for designs using mostly airbreathing first stages, because of the greater distance travelled and horizontal speed.

I'm pretty sure its best to do the retroburn on the flyback booster at apoapsis, as there it takes the least dV to reverse direction, correct?

I didn't fully go with a space-X, because ... well... wings/chutes in KSP aren't that heavy, and I'm not that accurate, and I want to return to the point of origin, not a floating barge not so far away from the point of origin.

I went with something more like one of the early shuttle concepts:

https://qph.is.quoracdn.net/main-qimg-673f5fdba0338ded2a95683fbe709421?convert_to_webp=true

Some early shuttle concepts included airbreathing engines for the landing phase, I added some but I wish to take them off to compare the states to pure rocket SSTOs.

It took me a while to get the ascent profile right, here were some earlier attempts:

My best results had the stack going vertical until about 150 m/s, then doing a gravity turn, ending with booster seperation at an attitude of about 45 degrees and an AP just out/nearly out of the atmosphere (this part is important so I can switch to the orbiter after the retroburn... no switching vessels while in the atmosphere!)

Anyway, the orbiter detaches and continues burning to put the AP up, when out of the atmosphere, I switch to the flyback booster, transfer some fuel and unlock some fuel tanks, and retroburn near its apoapsis.

Finish orbital insertion:

51 ton payload

Switching back to the booster while its still high in the atmosphere allows descent rate to be slowed and a guided glide back to KSC

I used the panthers a little to assist in getting a glide to KSC as above... but its descent rate was too high during the glide phase, and I had to light them again to level off for landing:

Touchdown speed was rather high, and I just rolled back to the runway:

 

I'm looking to get rid of airbreathers... I think I'll put aerospikes in their place... increase the wing area on the booster (using the 1200C heat tolerance "airliner" wings instead of the "shuttle" wings should be fine), and see what I can do... I'm really hoping that this can beat the cost per ton of disposable launchers, and the cost/ton and payload fraction of pure rocket SSTOs.

Has anyone else made functional flyback boosters?

What's your cost/ton and payload fraction for them?

[Brainlord Mesomorph]

My SSTO rocket can lift a payload and do a single "sub-orbit"  

If I put in orbit with an Ap of 88 km 90 degrees to the East of the KSC, and a Pe of 55 km 90 degrees to the west of the KSC , it pretty much just falls to the KSC.

Last time I added it up I was at about 550 to 600 funds/tonne.

 

EDIT: but I've been re-thinking this:
It costs about 20,000 funds to turn a dumb, disposable rocket into a autonomous recoverable rocket. (probe-core, chutes, etc) Now if you get back to the KSC, that's all free. BUT: if anything goes wrong... 

If the rocket comes down on the far side of Kerbin (because I overloaded the payload) of worse yet, the thing tumbles in reentry and the probe core overheats, then I lose the whole thing (including the extra $20,000). I've realized that if I fail 30% of the time, I'm obliterating all the money I saved on the recovering the other 70%.

And if I don't care about getting it back, I can put another 5 or 10 tonnes of payload on the damn thing.

So,, maybe not.... 

 

/physics is a big tease. Every time I think I'm saving money or dV in one place, I realize I'm spending it somewhere else.

Edited May 13, 2016 by Brainlord Mesomorph

[Warzouz]

FYI, my recoverable SSTO rocket have a payload mass ration from 15% to 19% depending on the model.

More details here

 

[KerikBalm]

Well, what you just described is a SSTO rocket, and your 20k thing only works if the entire rocket is 1 stage... I've seen disposable rockets getting below 600 funds per ton... which is pretty impressive.

SSTO rockets are fairly cost effective, but fuel costs are pretty high. I was hoping I could reduce fuel costs by staging away some deadmass.. although then I need to arrest that deadmass and send it backwards. I wonder what the best cost per ton has been for recoverable SSTO rockets... I haven't found any good thread about this (though I thought I saw one before).

I'm sure i can improve the cost by getting rid of the mk3cockpit... and for the challenges, the payloads are often inline oretanks, not a more practical cargobay (and most challenges don't require you to land the SSTO to qualify for the SSTO rocket category)

 

[Brainlord Mesomorph]

33 minutes ago, KerikBalm said:

 

Well, what you just described is a SSTO rocket, and your 20k thing only works if the entire rocket is 1 stage... I've seen disposable rockets getting below 600 funds per ton... which is pretty impressive.

 

That is the definition of SSTO. And that is what I'm saying esp if you factor in the cost of the occasional loss of these more complex, more expensive lifters.

 

Seperately I am working on a spaceplane concept that lifts large payload modules, (i.e. 100 tonnes in a fairing) to LKO. More details on that soon...

[KerikBalm]

yea, so I'm trying to reduce the cost of a non-airbreathing launch system by using the efficiency bonus of staging combined with the cost savings of recovering parts. At least in this case, while total failure rate may be the same, its not such a catasrphic loss for any one event - if you crash the booster, the orbiter is still intact, and vice versa.

Failure rate could be higher due to gameplay limitations... don't get your booster out of the atmosphere... and you can't switch back to the orbiter... you may lose the orbiter before you can land the booster.

This whole thing would be made much easier with one of those mods that will let you fly the booster back in a seperate instance, and then merge the two saves... but I'm looking for a pure stock solution... so my first stage booster needs to get its Ap above 70km.... failure to do that may force you to choose between losing the booster, or losing the orbiter.

Warzouz... those are cheaper with better fractions that I expected... when 1.0 came, I remember only seeing ssto rocket designs in the 10% range... good job.. my rocket is rather big for just a 51 ton payload... comparable to your RR-050 3x mainsail design... any it only beats your design if if gets a 100% recover and yours gets a 90%.

Although mine was overengineered as evidenced by the excess fuel in the orbiter, and the payload being lifted into well over a 100km orbit.

That 3.5 ton mk3 cockpit needs to go... a probe core, battery, and a rxn wheel can replace it much better... the RCS system needs to go... I can probably get away with lighter main landing gear... etc...

I wish the 1200K limit wings were lighter per unit lift than the 2400K wings, and I could save mass on the booster by using them

Edited May 13, 2016 by KerikBalm

[Warzouz]

Hmmm, that's why recoverable SSTO rockets are easy. Same flight profile all the way up (no bother about flipping due to staging the fins ; no strong TWR variation). As for the recovery part, if you're able to land around KSC, you can easily get 97% of dry value (this is my average)

My line of rocket average cost per to is from 360 to 440 (ignoring the 15T launcher with is worst than the other). Those launcher are also very scalable. You can double the payload from a model in 10 to 145 minute and do a success flight at first shot.

I even find SSTO rockets too easy and decided not to use theses in my current career.

 

[KerikBalm]

Yea, my career I was using SSTO planes, but I've started changing to VTOL SSTO rockets for convenience... but with turboramjets assisting the rocket engines... the turbos also help aiming the rocket at the KSC.

So... now my goal is a no-airbreather, 2 stage, less than 360 funds... this *should* be more cost effective than a SSTO rocket (and lets forget airbreathers, they are way OPd).

Its too easy to bring things down from orbit I guess, one reason we don't have reusable SSTOs IRL is that none of the rockets capable of SSTO (with horrible payload fractions though) would survive reentry (nor could they land again). I think as dV requirements go up, this way should become more attractive as a SSTO design runs into Tsiolovsky's tyranny.

[Raideur Ng]

While recovering 100% would be nice, it ends up being a hassle for every launch. Either using a SSTO heavy lifter or using a recoverable first stage that lands near the peninsula east of the KSC are the least painful ways to reuse your stuff. Unless this is simply a challenge, then anything goes.

[Alshain]

7 hours ago, KerikBalm said:

Has anyone else made functional flyback boosters?

Scott Manley did some time ago.

 

[KerikBalm]

54 minutes ago, Raideur Ng said:

While recovering 100% would be nice, it ends up being a hassle for every launch. Either using a SSTO heavy lifter or using a recoverable first stage that lands near the peninsula east of the KSC are the least painful ways to reuse your stuff. Unless this is simply a challenge, then anything goes.

Yes, its simply a challenge... Just like when I was making an STS style shuttle.

In that case, due to gameplay limitations, I recovered the ET (east of KSC, like you mention) rather than the SRBs. This is just for the fun/challenge.

Airbreathing SSTOs can't be beat for cost to orbit or payload fraction (well, airbreathing staged designs can do better I suppose)... but as you may have picked up that I was trying to avoid using airbreathers.

 

44 minutes ago, Alshain said:

Scott Manley did some time ago.

 

Thats not really the same... His design is just a demo and requires the mod "flight manager for reusable stages" (his words) to recover all the boosters.

My design works fully stock