Parachutes, suicide burns and the new Kerbal economy.

[Aethon]

Since the forum's been so sparse lately I thought I'd reflect on booster refunds. In .23.5 I had all these reusable lift stages tweaked and ready to be duplicated with the .24 parts, but they turned out to Op(riced) when S(olid)R(ocket)B(oosters) are so cheap.

I never leave debris, so the center stacks of my lifting stages are probe cored with enough fuel to de-orbit. During the .24.2 career play through, I found funds not that hard to come by. If I used a mainsail on a couple of tanks for a center stack, I could easily recoup the cost of ditching this by fulfilling a couple contracts during the launch. However, providing the lift core with enough 'chutes to safely land for recovery, kicked my dv in the efficiency minded coniglianos due to the added drag. At first I would follow them down and practice my suicide burns ( occasionally saving some and getting a lot better at suicide burns ) then I realized that with just two radial chutes I can slow way down ( from the usual 120m/sec impact speed, which isn't much from orbit, thanks to the 'motor oil' like stock atmosphere ) and use a short burn to save the stage.

Funny how speculation about a new update can be completely useless.

What say ye??

Edited August 18, 2014 by Aethon

[Pecan]

More or less the same - I'm playing around with SSTO rocket designs at the moment. I've found two drogue parachutes more effective in performance and cost than the others. With a SSTO/stage as light as two (almost empty) orange tubes and a mainsail they'll bring the speed down to ~20m/s so you need hardly any residual fuel to reduce to a safe landing speed.

What I haven't done yet is determine whether all the fuel burnt by using a SSTO design is less than the cost of (disposable) SRBs. Certainly it's cheaper to build an SRB-based rocket but I'm still only at the stage of comparing different LFO engines for SSTO payload ranges and comparing their costs (ie; are 5 mainsails more cost-effective than two KR-2Ls for launching a 50t payload?) ... results will follow when I have enough data to publish.

[Taki117]

As soon as I can unlock the parts in the tech Tree (I haven't even been to the Mun yet) I will build my favorite LKO SSTO. Capable of putting small satellites into orbit It will serve as the backbone to my light lifting needs.

[Monger]

That is an interesting notion... that landing in a controlled manner might actually be cheaper than just covering the part with chutes.

I have to admit, I never made my middle stage recoverable before 0.24. And I found it surprisingly difficult to do so. You need some kind of balancing and braking mechanism. I ended up with attached landing legs and more or less balanced parachutes, but now I can land a small middle stage even with some fuel in it.

If you are right, that the added drag actually turns out to lower efficiency, it might actually be useful to soften the landing with Vernier engines, or similar. Hm, I'll have to try that some time.

[Aethon]

I'll do a sim and take some screenies for an example, if someone can link me to a post on using the aerospikes. ( Over 1000 hours in and I tested one for the first time today. Shouldn't they get their oxidizer from Kerbins atmo?? I'm missin' something here. )

Edited August 18, 2014 by Aethon

[problemecium]

I dunno... I've been using exclusively reusable lift rockets and I'm currently rolling in way more money than I know what to do with.

[Laie]

That is an interesting notion... that landing in a controlled manner might actually be cheaper than just covering the part with chutes.

Chutes alone are horrible. For most parts, the safe speed is around 6-7m/s -- getting that slow on chutes requires a vessel to be 5-10% chutes by weight.

I like my craft to be mostly recoverable, but I'm not above slapping on generous amounts of boosters for a lost first stage. The remaining vessel is smaller, hence easier to design and recover. I don't know if they are the *most* economic solution, but they're cheap enough that I don't care. Transmitting science from somewhere, once, will take little time and buy you a lot of boosters.

[magnemoe]

More or less the same - I'm playing around with SSTO rocket designs at the moment. I've found two drogue parachutes more effective in performance and cost than the others. With a SSTO/stage as light as two (almost empty) orange tubes and a mainsail they'll bring the speed down to ~20m/s so you need hardly any residual fuel to reduce to a safe landing speed.

What I haven't done yet is determine whether all the fuel burnt by using a SSTO design is less than the cost of (disposable) SRBs. Certainly it's cheaper to build an SRB-based rocket but I'm still only at the stage of comparing different LFO engines for SSTO payload ranges and comparing their costs (ie; are 5 mainsails more cost-effective than two KR-2Ls for launching a 50t payload?) ... results will follow when I have enough data to publish.

I did some calculations, my light lifter in 0.235 used an 1x2 with two side mounted orange tanks for balance, added some extra pancakes on top and it could put 10 ton in orbit and land at spaceport. in 0.24 I use a skipper+ orange tank and 4-6 SRB instead, this is a bit cheaper and has the benefit that the unit cost is also far lower so if something goes wrong you looses less money.

I agree that two drogue parachutes is the most effective way to land, it will also let the crew survive an landing if out of fuel.

[FonVegen]

I'll do a sim and take some screenies for an example, if someone can link me to a post on using the aerospikes. ( Over 1000 hours in and I tested one for the first time today. Shouldn't they get their oxidizer from Kerbins atmo?? I'm missin' something here. )

Nope, Aerospikes work just as your regular rockets and thus do NOT count as jet engines, meaning they can't use Intake Air.

[Aethon]

Promised screenies.

I haven't used the arm parts much but this applies to them as well. Kinda wanted to show my new Tarsier space telescope. Note the dv and vehicle cost with only 2 'chutes.

http://steamcommunity.com/sharedfiles/filedetails/?id=302440114

and with many 'chutes.

http://steamcommunity.com/sharedfiles/filedetails/?id=302441250

http://steamcommunity.com/sharedfiles/filedetails/?id=302441633

I think the blast deflection plates aren't allowing the speratrons (sepatron) to work. It's a close thing,

http://steamcommunity.com/sharedfiles/filedetails/?id=302442097

but they keep sep exhaust from damaging the rest of the ship.

http://steamcommunity.com/sharedfiles/filedetails/?id=302442999

Throttle control keeps the time to AP between 40 and 50 seconds and inside the velocity vector for an efficient launch. This would prob. be better with a skipper on smaller loads though the mainsail went like hell til 20,000m or so.

http://steamcommunity.com/sharedfiles/filedetails/?id=302443696

Shut 'er down clown.

http://steamcommunity.com/sharedfiles/filedetails/?id=302445703

Six and some minutes to AP for a 1 sec. circ. burn. Nice profile. Load dumped in LKO. Will transfer to HKO out beyond Minmus with it's LV-909.

http://steamcommunity.com/sharedfiles/filedetails/?id=302449114

Shooting for a daylight splashdown near the space center.

http://steamcommunity.com/sharedfiles/filedetails/?id=302449985

Yes Jeb. It would be prettier with clouds.

http://steamcommunity.com/sharedfiles/filedetails/?id=302450581

Speed and fuel remaining just before the 'chutes pop. Haven't lit the engine since the deorbit burn.

http://steamcommunity.com/sharedfiles/filedetails/?id=302451277

Good 'chutes.

http://steamcommunity.com/sharedfiles/filedetails/?id=302452062

Short burn. If on land, recover quick 'afore it falls over.

http://steamcommunity.com/sharedfiles/filedetails/?id=302452456

Results.

http://steamcommunity.com/sharedfiles/filedetails/?id=302453114

Edited August 22, 2014 by Aethon

[Pecan]

...in 0.24 I use a skipper+ orange tank and 4-6 SRB instead, this is a bit cheaper and has the benefit that the unit cost is also far lower so if something goes wrong you looses less money.

My current 10t SSTO also uses the skipper, although in my case 2 skippers with X200-32 and -8 tanks (adapters and drogues) radially mounted to a core jumbo-64. You're replacing a skipper engine, (the equivalent of) a jumbo-64 and X200-16 (cost ~18,850) with SRBs (say 6 to be conservative = 10,800?) so should be around 8,000 cheaper at launch. My engine and empty cans are worth about 5k after recovery (these are very rough figures, I'm just sketching things here!) so per launch your design could be about 3,000 cheaper, I think.

I won't be able to test until tomorrow but it seems plausible that disposable SRBs are cheaper long-term as well as immediately. Please let me know if you test and compare before then.

Oh, and it is a very good point that if things go wrong my design means much more lost capital. But what could go wrong ... ?!

[magnemoe]

My current 10t SSTO also uses the skipper, although in my case 2 skippers with X200-32 and -8 tanks (adapters and drogues) radially mounted to a core jumbo-64. You're replacing a skipper engine, (the equivalent of) a jumbo-64 and X200-16 (cost ~18,850) with SRBs (say 6 to be conservative = 10,800?) so should be around 8,000 cheaper at launch. My engine and empty cans are worth about 5k after recovery (these are very rough figures, I'm just sketching things here!) so per launch your design could be about 3,000 cheaper, I think.

I won't be able to test until tomorrow but it seems plausible that disposable SRBs are cheaper long-term as well as immediately. Please let me know if you test and compare before then.

Oh, and it is a very good point that if things go wrong my design means much more lost capital. But what could go wrong ... ?!

Well landing on the edge of the runway is one, this tend to cause the rocket to tip over.

[stupid_chris]

Chutes alone are horrible. For most parts, the safe speed is around 6-7m/s -- getting that slow on chutes requires a vessel to be 5-10% chutes by weight.

I like my craft to be mostly recoverable, but I'm not above slapping on generous amounts of boosters for a lost first stage. The remaining vessel is smaller, hence easier to design and recover. I don't know if they are the *most* economic solution, but they're cheap enough that I don't care. Transmitting science from somewhere, once, will take little time and buy you a lot of boosters.

This is only true if not using RealChute

[problemecium]

I still plaster the sides of my lifters with chutes for those times when I reenter with no fuel left, which happens a lot lately thanks to my attempts to put gigantic payloads in space.