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Falcon 9R, KSP Style - Reuse Everything

Jarnis

By Jarnis
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Jarnis

Jarnis

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So, Bill kept wanting to fly over and over again and KSP was rapidly running out of boosters (accidents, Jeb doing his thing and so on...). Those things cost some real money and with the whole thing thrown away every time, Bill just couldn't get a rocket to fly again and again... Then someone found an interesting video from some competing Space Business... I of course mean this one;

"Hey, we can do that, can't we?"

Bill could immediately see the benefit. If you just landed the stages back to KSC under rocket power, they could be refueled for another go in no time. Bill could get to fly a rocket every week!

"Landing a rocket stage back on launchpad. I mean, how hard can that be?"

Now at first I thought such a mission profile would not work in KSP because you can't be piloting two things at once - once you ditch first stage, you need to be flying the upper stage to orbit while the first stage falls down. But I really wanted to see how it would look like when a massive first stage simply turns around and tries to fly back to the pad. After bit of experimentation I saw a way to run a suitably steep trajectory and get the upper stage high enough before the first stage re-entered and got wiped out and... After some half-dozen dry runs to get the timings of everything down...

Presenting my humble attempt to re-enact Falcon 9R mission profile in KSP:

It really works! And the fuel required for stage landing is almost nothing. Sure, payload mass will be lower per launch but stage re-usability would make it worthwhile. Save for the potentially iffy bit of heat shielding the second stage properly so it survives re-entry intact, it should work. Can't wait for SpaceX to try it for the first time (starting with Stage 1 recovery without legs to a kinda-soft ocean landing at some point later this year).

Probe bodies and RCS systems in all stages to keep them controllable. All stock except for MechJeb. Even SpaceX will use computer programs to control missions and landing stages with almost no fuel margin is not something you'll be able to fly manually anyway.

Payload is obviously tiny but I can't see why this couldn't be scaled up some more.

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Pursuedtank

Pursuedtank

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Nice one. I do like doing power landings. Are you ever going to end the flights of those first stages that you have sitting near the launchpad or leave them as a monument to your success?

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Jarnis

Jarnis

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Nice one. I do like doing power landings. Are you ever going to end the flights of those first stages that you have sitting near the launchpad or leave them as a monument to your success?

It's a separate "new game" just for this experiment so they litter the pad area only in this save. And they sure look cool.

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Jarnis

Jarnis

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Jeb got seriously envious of Bill and his rapidly re-usable rocket and wanted to have a go as well. To avoid a fight, KSP engineers decided that they needed a three-man capsule. That meant a bigger rocket.

So... after a bit of tinkering and some test flights that ended up with massive stages going "splash" just short of the KSC, here is the upscaled rocket, a "Heavy" of sorts. No separate side stage recovery because, well, KSP can't manage that (side tanks would have to go away far too early and no way to control two things at once). But this thing manages a three-man pod with enough fuel to do a simple "recrew space station" mission with every stage (including the capsule) capable of powered landing at KSC.

Same flight plan, except first stage arcs only to 67 degrees after 10km altitude and stages at the instant the velocity indicator auto-switches from "surface" to "orbital" (~920m/s which suddenly flips up to 1000m/s+ orbital). Need a bit steeper climb because the stage is so much larger - all that drag.

Both stages recovered;

026gX4v.jpg

Rocket on the pad;

jGaXMYx.jpg

Still a fairly small payload but nothing says this couldn't be upscaled further. The only real limitation is that you need a massive first stage as it has to be able to get high enough to give you a long enough "lob" upwards after staging so you have enough time to deposit the upper stage to a provisional orbit before first stage goes "poof".

As KSP is lacking the oh-so-needed "medium" large engine, had to resort to a fairly exotic dual-engine config for the upper stage. On the plus side, the girder contraption that allows attachment to the lower stage also provided a nice place where to stick a pod core, batteries and MechJeb :)

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Jarnis

Jarnis

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Very neat. I like it a lot. I suppose you could add SRBs with parachutes to give the first stage an extra push.

No parachutes is my motto. SpaceX doesn't plan to use them for landings on the ground (except as backup for the capsule) so I won't use them either.

Also solid rockets and human rated rockets don't mix very well :)

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Uncle Mort

Uncle Mort

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No parachutes is my motto. SpaceX doesn't plan to use them for landings on the group (except as backup for the capsule) so I won't use them either.

Also solid rockets and human rated rockets don't mix very well :)

Fair enough, perhaps someone should mention that to NASA.

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Jarnis

Jarnis

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Fair enough, perhaps someone should mention that to NASA.

:ChallengerGoingBoom.jpg:

I believe they know.

Had that been a liquid engine booster, first of all it would not have had a joint to leak and had any problem developed, the engine would have been shut down. Would still have been a bad day but at least there would have been a theoretical RTLS abort scenario that would have involved some highly untested procedures. At least such an abort could have, in theory, saved the crew.

...and the reasons for using solids (both on the Shuttle and on the upcoming SLS - if it ever flies) are not entirely due to cost or technical reasons. There are politics involved (Thiokol/ATK being a big well-connected arms manufacturer, solids being a better idea for long storage times and required rapid launch capability of ICBMs and all that). At least SLS/Orion will have launch abort capability with the escape tower. But that's already fairly off-topic...

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magnemoe

magnemoe

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Tested this a bit, using the novapunch parts as I want an useful payload, else I could just as well used an jet powered first stage. This takes 70 ton to 100km.

Main issue was that the first stage would either has to be dropped before or early in gravity turn, or very late. I ended up using two boosters who is dropped before gravity turn and an main stage who is dropped at the end and can land on another continent. Optionally if the cargo is light I might let it go into orbit and deorbit to land at spaceport.

At launchpad.

screenshot1d.png

Landing booster at spaceport.

screenshot2b.png

Main stage flight path, I braked a bit to land on ground.

screenshot5.png

Landing main stage

screenshot7b.png

The top of the stages is the reentry packages, contains fuel for landing, mechjeb autopilot. rcs and gyros. I might reduce the size for the boosters as they don't need so much fuel, just enough to brake from 140m/s then landing. For an even heavier rocket I might use four boosters.

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Jarnis

Jarnis

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Won't that design cause you to lose one of the side stages? I mean I assume you ditch them simultaneously but cannot steer both to a landing? Or are you madly switching between them while keeping them within 2.5km of each other?

Also I guess that your plan kinda doubles up as the potential flight plan of the planned re-usable Falcon Heavy. (Falcon HeavyR?) - two side cores ditching early and crossfeeding to the core, then returning to launchpad while the center core goes much further downrange and lands... somewhere else. Floating barge? Across the Atlantic?

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magnemoe

magnemoe

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Won't that design cause you to lose one of the side stages? I mean I assume you ditch them simultaneously but cannot steer both to a landing? Or are you madly switching between them while keeping them within 2.5km of each other?

Also I guess that your plan kinda doubles up as the potential flight plan of the planned re-usable Falcon Heavy. (Falcon HeavyR?) - two side cores ditching early and crossfeeding to the core, then returning to launchpad while the center core goes much further downrange and lands... somewhere else. Floating barge? Across the Atlantic?

As you can only control one booster you lose the other, you also lose the upper stage if you control the booster, so this is just proof of concept and role playing. as the landing fuel is stored separately I don't have to think about it during normal launches

Current falcon 9R will recover the first stage, long term plan is to recover the second also. For falcon heavy the boosters should be very attractive to recover as they are dropped earlier than the normal first stage, the first stage is released higher but have no idea how high. As SpaceX plan to launch from Texas they might be able to land in Florida

One thing I learned was that return to pad cost a lot of dV, you have to cancel horizontal movement and give you enough speed to get back, yes if you wait with the burn until you get lower most of the horizontal speed has gone but you has twice as long to get back and air resistance, you only need around 200m/s to land

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Jarnis

Jarnis

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My original video actually worked around the KSP limitation by using a very steep trajectory; During the time the upper stage is being driven to a preliminary orbit, the first stage is still going uphill and I get to return to control it around the time it reaches apogee.

The fuel required to return to pad from there is less than 10% of the total fuel load of the first stage (both boostback and landing)

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Jarnis

Jarnis

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Also btw starting with the Falcon 9 v1.1 they will try doing a soft water landing, first v1.1 flight is in june I think!

Yep, tho I guess for this first one the attempt is more like "Try to get the stage down without it breaking up when falling down". Kinda-soft water landing would be icing on the cake. Recovery of anything even more so. Probably will take few flights before they get it all right but hey, the stages were going to be tossed anyway so "free testing", so to speak.

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