Challenge: Reusability Extreme
Due to the cost-effectiveness of private aerospace, the Forum has had its budget slashed and such arguments as “If SpaceZ can do it for 50 times cheaper, why even bother?” have been thrown around. Therefore, we have decided that to remain competitive, we must develop our own fully reusable launch system, and do something spectacular with it.
Normal Mode:
Land a fully reusable rocket on The Moon and return with less than 30 parts.
Hard Mode:
Land a fully reusable rocket on Mars and return with less than 20 parts. (must include capsule)
Super Mode:
Why not both...?
Video is finally ready.
A Disclaimer.
Firstly: My rocket actually has 21 parts.
There is a probe core buried on the first stage which I forgot about after testing before the mission started and only noticed it during video editing. It makes no difference to the job really since I never control the first stage once the upper section is separated. But if anyone is going to get excited about it I'm more than happy to re-do the mission minus the 2.5tons of dead weight on board to prove a point.
Secondly: I done it in 1.4, not 1.5. Why? Cos I'm not done with 1.4.06, that's why. And before someone starts whining about the different solar system sizes and it's easier in 1.4, I'm going to say 'check the Dv map'. The actual budget from LEO to the moon is almost the same, give or take a few m/s (821m/s to 829m/s). Same with to Mars (1,154m/s to 1,205m/s. Now balance that against me using a broken drag system (I'm not sure what the 1.5 LEO figure is, but I'll put money it isn't even close to 3500+m/s...)
and less efficient engines and tell me it's easier. And yeah, drag is properly on. I start at the menu screen and you can tell it's on cos I'm not supersonic until 10km up.
The tale then.
If you're gonna do re-usable, then you need to actually re-use the rocket.
It's something that gets said a lot, but how many of you actually re-service your launch systems in-game? I suspect not as many as there are 're-usable' rockets around, that's for damn sure. And this is supposed to be a SpaceX company mission goal, fully re-usable, rapid turn around rockets. The idea is they want to be able to launch, land, top up the tanks, bang a new payload onboard and send it straight back up.
So that is pretty much what I was going to do, even if the challenge itself was quite...restrained...in its aims.
Looking at the challenge criteria, 20 parts sounds like it's supposed to be some kind of smart limitation on size whilst totally forgetting that even 5 fuel tanks is nearly 450 tons of mass in 1.4, and in 1.5, it's even more (600tons). So fuel mass / Dv was never going to be an issue.
What it did do though was limit toys you could bring along to facilitate that 're-usability'. Docking ports, staging, parachutes, engines, landing legs etc.
Because of that, this required a simple but not light approach, which is why I went with an SSTO style design for the first part.
Then, the lander itself. The smaller I could make it the better, so a grasshopper, enough fuel to do powered landing and take-offs with landing legs on the side. And then an orbital re-fuel tank that it'd push around the solar system, leave in orbit, land, launch, RV with, dock and then push back. This approach lowered the overall mass considerably, keeping the SSTO launch mass down.
I also decided that RCS is too mainstream and went with main engine docking manoeuvres. Cos I can. This has the advantage of not only further reducing part count, dry weight
and aerodynamics, but also fuel if you know what you're doing.
Kerb weight is about 300tons, maybe less. I could've got it to about 200 with a 2 stage launch system, but that pushed me over the parts threshold (ironically) and wasn't viable.
Then it was a simple case of putting legs under it, building a re-fuel truck for it, testing to see if it can be landed, connected to the truck and then re-launched before starting the mission.
It's fucking ugly though, and I've got a
beautiful Uranus IB set up with a much better looking truck as well in-case I get bored and want to do the mission again.
The mission itself goes as thus:
- Spawn on the pad and blast into a very low orbit with the SSTO.
- De-couple the Lander and fuel tank, burn TLI to the moon.
- Rather than bring everything down to LLO, to save fuel I circularised to a rather eccentric orbit facing back out towards Earth.
- Left the fuel tank upstairs and powered landing to the surface and blast straight back to another low (350m ish) orbit.
- Grab an encounter (with a 200m/s speed difference), dock (without RCS) and then TEI back to Earth
- Aerobrake, make an encounter with the SSTO still sitting empty in LEO, dock (after cancelling out the enormous orbital speed difference)
- Transfer the remaining fuel to the SSTO
- De-orbit
- Powered landing onto the Launchpad
- Mission One complete
- Re-fuel SSTO from fuel truck.
- Launch to LEO again
- Decouple and burn TMI to Mars aerobrake
- Again, no point bringing the fuel tank all the way down so aerobrake until the orbit is facing back out towards Earth, raise the periapsis until it's above Mars atmosphere
- De-orbit, parachute landing and straight back up to LMO
- Encounter and dock with the fuel tank
- Burn out of the SOI and lower the perihelion to Earths level
- Get a decently close approach and adjust with deep space burns to encounter
- Aerobrake
- Set up docking encounter with SSTO in LEO
- Dock with SSTO and transfer fuel (if you look closely enough, my encounter orbit puts me at 28.5km periapsis and have to do some adjusting on the fly cos I can't go around again. I make the dock at 30.4km...
- Pre-landing fuel transfer and de-orbit burn
- Powered landing at the launchpad
- End of Mission Two
- Re-fuel SSTO from truck and launch back to LEO.
Rinse and repeat.
As Steve puts it,
If I'm honest, making the video was harder than the challenge itself. Condensing over an hour of silent footage into an 11 minute video with added and properly timed sound effects took
ages. But I'm pretty happy with both, especially as it's the return of the NoPro brand hehe.