Reuseable rockets

[Jonfliesgoats]

Anybody want to share their latest and greatest reuseable rocket designs?  It seems like KerbalX is loaded with spaceplanes.  Even birds tuck in their wings when they are done using them!  For those of us who think it's silly to lug wings into the vacuum of space, let's share ideas!

(This is a shameless attempt to improve my own reuseable rockets on Xbox.)

[TheKosmonaut]

Funny, I was just playing around with a stock New Shepard design the other day. I don't have it complete yet as i find it to be a bit on the ugly side (Frankly so is NS) but will update again with an album later. For now, here was a shot from the launchpad!

 

I just realized that the engine is not stock, but you should be able to get similar results with the stock engines no problem!

[valens]

My own take on recoverable first stages/boosters. Although most of them incorporate expandable SRBs, these can be removed for lighter payloads.

Phaeton-R is a bit more advanced these days (R-1V/6), due to the mad resistance of 3.75 m parts.

29 minutes ago, TheKosmonaut said:

Funny, I was just playing around with a stock New Shepard design the other day. I don't have it complete yet as i find it to be a bit on the ugly side (Frankly so is NS) but will update again with an album later. For now, here was a shot from the launchpad!

BTW, is that a Skipper under that fairing?

Edited October 29, 2016 by valens

[Jonfliesgoats]

I play on Xbox and am at work ATM, so pardon my lack of screenshots.  I agree about NS being a little fugly.  Also, my standard reuseable rocket can only get about 7 tons to LKO, maybe more if I fly a nice gravity turn.  I can get that up a lot with disposable SRBs.

Have you been using heat shields or just burning retrograde when you hit qmax?  (Maximum aerodynamic pressure and heating).  From the shots I see, there is little for heat shielding.

I use tons of parachutes, and try to splash down near KSC.

I wonder if it's more efficient to carry fuel for a powered landing or parachutes?  There has to be some crossover point in mass. 

Edited October 29, 2016 by Jonfliesgoats

[Jonfliesgoats]

better question:

Am I flying an efficient landing?  I use aerodynamic braking fine tuned with speed brakes to get a 20t dry mass rocket down to about 3000m and 300 m/s over KSC or Booster Bay, then deploy parachutes.

I have neglected the math on this phase of flight!  

Edited October 29, 2016 by Jonfliesgoats

[TheKosmonaut]

@valens Ah, I said it was stock but realized that it is actually a SpaceY K1 "Kiwi" engine! Oops. You should be able to get similar results (though w/ much higher twr) with the Vector or something like that.

[valens]

38 minutes ago, Jonfliesgoats said:

Have you been using heat shields or just burning retrograde when you hit qmax?  (Maximum aerodynamic pressure and heating).  From the shots I see, there is little for heat shielding.

I use tons of parachutes, and try to splash down near KSC.

 

25 minutes ago, Jonfliesgoats said:

Am I flying an efficient landing?  I use aerodynamic braking fine tuned with speed brakes to get a 20t dry mass rocket down to about 3000m and 300 m/s over KSC or Booster Bay, then deploy parachutes.

With the AIRBRAKES, both boosters slow very efficiently in the high atmosphere, so heat shields were not really necessary. However, one key aspect of my re-entry profile is gyroscopic stabilization of the booster: entering the atmosphere with SAS off and all control surfaces fully deployed takes the booster into a fast spin, which stabilizes its trajectory and preserves the AIRBRAKES at the same time.

The thing is that your engines are already rated for quite high temperatures, so they should take the brunt of the heat. Airbrakes, though... Hence the spinning.

As for the weight aspect, Herakles-R weighs about 37 tons when dry, and uses 8 drogues and 12 chutes to land (though I should check if the chutes are enough — imho they should). I try to avoid splashing down, though, as the booster often topples and breaks. 

12 minutes ago, TheKosmonaut said:

You should be able to get similar results (though w/ much higher twr) with the Vector or something like that.

The latest iteration of Phaeton-R uses indeed a Vector with 30% gimbal to improve the ∆v.

Edited October 29, 2016 by valens

[Jonfliesgoats]

Very cool, valens!  I have tried rotating re entries to distribute heat but but always did it with a slow rate, which probably wasn't fast enough.  From LKO I have recovered rockets without heat shields too.  I do wimp out and thrust to pass through qmax as quickly as possible (usually a burn around 25000 meters).

With regard to slashing down, I find my parachutes sequentially disappear, so the ones mounted high also slow that final tip of my rocket onto its side.

 

 

Also, guys, I started playing with my calculator.  Given a 20 ton rocket with a 280isp motor and speeds of 300m/s at 3000 meters altitude, I came up with the following landing fuel requirements.

A free fall to a single landing burn would consume a mere .4 tons of fuel.  Of course a second too soon or a second too late and your rocket explodes on landing.  Realistically, I think it would take about a ton of fuel to make a decent landing from a 300/3000 window.  This accounts for corrections, errors and a less suicidal profile below 100 meters.  Do these figures check with your experience?

So, assuming smoke sloppy flying, having more than a ton of parachutes becomes wasteful and a landing burn or combination thereof becomes more efficient, right?

Edited October 29, 2016 by Jonfliesgoats

[Jonfliesgoats]

My reliance on parachutes is a display of my rocket-cowardice.

How cool would it be to have altimetric switching in stock to initiate some of these burns?

Edited October 29, 2016 by Jonfliesgoats

[Jonfliesgoats]

Each radial parachute can support about 1.7 tons at about 10m/s at sea level on Kerbin.  So a 20 ton vessel should require about twelve parachutes (which is in line with what I use.) to safely splash down.  So I am carrying 1.2 tons of parachutes alone!

If reduce my parachute load to only lower my craft under canopy at 20 meters per second, each radial parachute should be able to support a little more than six tons.  That means only three or four radial parachutes would be required and a teensy burn at touchdow would slow my craft to a survivable landing!  I could save .6 or .7 tons!  Only .4 tons of fuel Can slow from 300/3000.  Only trace amounts of fuel would be required for that final slowdown on touchdown!

Have you guys experimented with rocket assisted parachute recoveries?  It seems this is a nice way to save weight without carrying large reserves of mulligan propellant.

I bet I can seriously reduce my funds spent on SRBs!

Edited October 29, 2016 by Jonfliesgoats

[Rune]

2 hours ago, Jonfliesgoats said:

Each radial parachute can support about 1.7 tons at about 10m/s at sea level on Kerbin.  So a 20 ton vessel should require about twelve parachutes (which is in line with what I use.) to safely splash down.  So I am carrying 1.2 tons of parachutes alone!

If reduce my parachute load to only lower my craft under canopy at 20 meters per second, each radial parachute should be able to support a little more than six tons.  That means only three or four radial parachutes would be required and a teensy burn at touchdow would slow my craft to a survivable landing!  I could save .6 or .7 tons!  Only .4 tons of fuel Can slow from 300/3000.  Only trace amounts of fuel would be required for that final slowdown on touchdown!

Have you guys experimented with rocket assisted parachute recoveries?  It seems this is a nice way to save weight without carrying large reserves of mulligan propellant.

I bet I can seriously reduce my funds spent on SRBs!

That is the often overlooked cost of chutes: they are heavy. That, combined with the fact that you only get 100% recovery if you nail a precision landing, and the thermal dangers of reentry, has me convinced lately that the thing to do is VTHL (Vertical Takeoff, Horizontal Landing). At least in stock KSP, without insanely precise landing algorithms, and where SSTOing is (relatively) easy.

~50mT VTHL Booster:

Spoiler

~20mT VTHL Booster, side-mount version:

Spoiler

Granted, wings are useless in orbit. But for that size, I'm not using that many wings!

 

Rune. As a result, landings are somewhat sporty.

Edited October 29, 2016 by Rune

[Jonfliesgoats]

Very sexy!  

I am driving toward the math behind optimum rocket designs.  VTHL is cool.  Lugging whiplash engines, extra fuel tanks, intakes, etc gets out of control.  A lot is about my personal tastes, too.  After getting a spaceplane SSTO to orbit a few times, flying a long ascent and descent profile to put small payloads into orbit gets a little monotonous.  Reliable, reuseable rockets get lots of stuff to orbit quickly and have negligible increases in cost.

HOTOL has its place though.  It's just not my idea of fun after five or six times.

Also, I am more familiar with high performance aircraft, so fixed wing spaceplanes don't seem as exotic or exciting as rockets.  Again, this is just a function of my personal tastes.

[Rune]

5 minutes ago, Jonfliesgoats said:

Very sexy!  

I am driving toward the math behind optimum rocket designs.  VTHL is cool.  Lugging whiplash engines, extra fuel tanks, intakes, etc gets out of control.  A lot is about my personal tastes, too.  After getting a spaceplane SSTO to orbit a few times, flying a long ascent and descent profile to put small payloads into orbit gets a little monotonous.  Reliable, reuseable rockets get lots of stuff to orbit quickly and have negligible increases in cost.

HOTOL has its place though.  It's just not my idea of fun after five or six times.

Yeah, good ol' rocket power is convenient, ain't it? Besides, there's no way I'd have gotten that humongous ring station supersonic without it.

Anyhow, in math terms (that is, ideally), the most efficient thing would be a VTVL that splashes down in the ocean (so you save on landing gear). The thermal issue is tricky, tough. I dislike using airbrakes because of their own low thermal tolerance, so the only option is to make your rocket more draggy, with also hurts you on ascent. That is how I got myself into the wings thing, I wanted to keep the engines safe from blowing up. Then again, a ~500m/s burn on reentry should cost very little fuel. But the precision! Nah, I like being able to pilot my way out of situations, and have the time to manage my energy to a smooth runway landing.

 

Rune. It's usually no more than ~10mins, realtime, about the same as a rocket ascent+rendezvous.

[Jonfliesgoats]

A VTVL lifting body is an option.  All you'd need is a relatively low drag wedge, which launches easily enough.  Adjusting alpha on reentry would give you decent control and provide the benefits of a lifting reentry too.  I experimented with this successfully some, but had trouble scaling it up enough for the payloads I wanted to deliver.

Once subsonic, I would deploy parachutes and splash down.  

I had a similar problem with using speed brakes during a lifting reentry.  When I wanted to get less draggy, I would lower my alpha but the heats at my leading edge stagnation point would go sky high even from LKO.  Guess where my speed brakes/spoilers were?

If I could round off the leading edges a little more I'd get better heat distribution.

Edited October 29, 2016 by Jonfliesgoats

[Rune]

16 minutes ago, Jonfliesgoats said:

You a VTVL lifting is on option.  All you'd need is a relatively low drag wedge.  Adjusting alpha on reentry would give you decent control and provide the benefits of a lifting reentry too.  I experimented with this successfully some, but had trouble scaling it up enough for the payloads I wanted to deliver.

Once subsonic, I would deploy parachutes and splash down.  

If you go that way, I'd warn you that the tricky thing is to find the true Center of Pressure (CoP) of your rocket. The VAB/SPH lift indicator only takes into account the lift from wings, so all the body lift from the empty tankage will throw you off a lot (and towards instability, to boot). You'd be surprised how little wing you need to glide one big empty booster, if you save some speed to level off just before you hit the ground.

 

Rune. The 20mT booster wastes more weight on inefficient tankage than in wings and stuff (less than 2mT in wings and landing gear).

Edit: I actually did the math. Using that Mk3 fuselage instead of round ones, alone, is a 0.89mT hit. With all the other adapters included, over 2,5mT spent in useless aesthetic fluff. I stand by its necessity.

Edited October 29, 2016 by Rune

[Jonfliesgoats]

Already been down that way!  Actually the whole reason I had speedbrakes as far forward at they were was to provide more pitch control as the center of pressure moves with different angles of attack.  The design actually works great provided I don't lower my AOA too soon and start cooking my craft.  I am not opposed to a wee bit of wing on a vthl or vtvl design.  

Scaling up my vtvl lifting body was more of a challenge.  Perhaps I will return to it?As is my reuseable rockets only get about fifteen tons of payload to LKO.  7 tons if I am entirely reuseable.  

Edited October 29, 2016 by Jonfliesgoats

[Rune]

3 hours ago, Jonfliesgoats said:

Also, guys, I started playing with my calculator.  Given a 20 ton rocket with a 280isp motor and speeds of 300m/s at 3000 meters altitude, I came up with the following landing fuel requirements.

A free fall to a single landing burn would consume a mere .4 tons of fuel.  Of course a second too soon or a second too late and your rocket explodes on landing.  Realistically, I think it would take about a ton of fuel to make a decent landing from a 300/3000 window.  This accounts for corrections, errors and a less suicidal profile below 100 meters.  Do these figures check with your experience?

So, assuming smoke sloppy flying, having more than a ton of parachutes becomes wasteful and a landing burn or combination thereof becomes more efficient, right?

Ok, now I'm actually going to try and help you with your thing.

For VTVL rockets with legs (or without them), I usually just put a chute or two and be done with it. The force that the chutes give you is proportional to speed, so if you get them to make you fall only somewhat gently, that's when you are squeezing the most out of them. Semi-deployed, they stabilize you and get you somewhat subsonic.Then, you can use the full deploy of the chutes as a guide on when to start a powered descent, since they are altimeter-bound themselves (and you can mess with their full-deploy altitude, in case you want to develop a consistent suicide-burn sequence). With practice, you'll be able to use very little fuel for the final burn that way.

 

Rune. That should actually be the advice you are after the most. But I encourage you to try other things just the same! Everything gets boring with enough repetition.

[Jonfliesgoats]

Also, I imagine Jeb pointing straight up, nostrils nonexistently flaring as he makes unblinking eye contact with me.  I can't imagine Jeb delicately climbing to 20km, accelerating, pitching oh so gently skywards and only then belching flame and money out rocket bells.

Right!  Parachutes, drag in general varies geometrically with dynamic pressure.  I ran the numbers and saw I could get down to a SL vertical speed of 30m/s with only two radial parachutes and 20m/s with four.  

Up until now I have been massively inefficient with my parachutes.

 

Whoops!  Late for work!  I look forward to reading more of everyone's rocket insight!  Thanks for the help an conversation!

[Jonfliesgoats]

Okay, now I really have to go...

 

1 hour ago, Jonfliesgoats said:

Desired Vertical Speed (m/s) at Kerbin Sea Level.               Mass per Radial Parachute. (tons)

5                                                                                           .4  

10                                                                                       1.7

20                                                                                       6.8

40.                                                                                    27.2

 

[valens]

7 hours ago, Rune said:

~20mT VTHL Booster, side-mount version:

  Reveal hidden contents

Granted, wings are useless in orbit. But for that size, I'm not using that many wings!

I think this is a very elegant solution for this kind of problem (the only disdvantage I can see is having to deorbit and fly back 6+ boosters, which I guess can be a little boring). Just wondering though where is your control part and if this does not make ascent too challenging.

[Rune]

13 hours ago, valens said:

I think this is a very elegant solution for this kind of problem (the only disdvantage I can see is having to deorbit and fly back 6+ boosters, which I guess can be a little boring). Just wondering though where is your control part and if this does not make ascent too challenging.

Yup, they are actually eight pushing that station, so yeah, it gets old quickly. On the plus side, it gives you lots of practice? Nah, it's mostly a solution to needing a very distributed load to avoid RUD events pushing that thing through the atmosphere.

The control point is a probe with a reaction wheel and a fuel cell, right where the third engine would be in the tail, if there was a third engine that is. You kind of can see it in the pictures, if you look closely.

 

Rune. A comfy place to put heat-sensitive stuff.

[valens]

1 hour ago, Rune said:

The control point is a probe with a reaction wheel and a fuel cell, right where the third engine would be in the tail, if there was a third engine that is. You kind of can see it in the pictures, if you look closely.

I meant for the ascent. Is it the same?

Edited October 30, 2016 by valens

[Jonfliesgoats]

They are nice looking to be sure.  

[Jonfliesgoats]

So far it looks like my rockets have been in line with most of your designs, and this thread has been handy in convincing me to try a combined parachute-powered landing to minimize the amount of recovery mass I have to lug.  I ran some quick numbers and see room for improvement.

 

 

[Rune]

2 hours ago, valens said:

I meant for the ascent. Is it the same?

Oh right, you mean if I have some upwards-facing control point on the station itself. Sure! It has a crew cabin inside one of the cargo bays oriented "the right way", plus a lot of other stuff (a lab, refining facilities, tankage...).

1 hour ago, Jonfliesgoats said:

They are nice looking to be sure.  

One does one's best.

 

Rune. You guys know you can grab all these things in my KerbalX page, right?