Mission proposal: Return(?) to Laythe

[UH60guy]

I’m developing a second mission to Jool before my first one arrives. I figure we see a lot on the forum of how the missions themselves go or how spacecraft are built, but not a lot on the planning side. In the effort to share a different side of the design process, here's my pre-trip planning; I'll start a new thread when the mission launches.

History and Purpose:

A brave team of seven Kerbalnauts is en route to Jool, launched in Kerbin’s first interplanetary mission ever. That mission will probe the system, land four Kerbals in the ocean on Laythe, require two of them to remain in the Laythe Ocean Base and Buffet for an extended stay, and return five of the seven to the Kerbal International Space Station Bar and Grill in Kerbin orbit. Not wanting that surface stay to be too long, KSC is preparing to put together a mission to recover the two inhabitants, and to tour the Joolean moons while in the neighborhood.

Unfortunately, the launch window for the recovery/exploration mission comes well before the first mission’s ships actually arrive at Jool, so the planning will need to make some worst-case assumptions about the first mission's status and to build in rescue capability.

One problem encountered was the structural failure and separation of the Ocean Base interplanetary cruise stage’s main fuel tanks (full Jumbo-64 and X200-32 plus LV-N engine) after completing the Jool transfer burn. This led to a rendezvous with another ship in the convoy outside the orbit of Dres, and the subsequent rebuilding of the modular ships in deep space. It’s unknown now if there’s enough fuel to get the first crew home, but KSC thinks they’re OK.

Mission profile:

• Get all components into space without exploding too much.
  
• Transfer to Jool and aerobrake without burning the marshmallows.
  
• Transfer to Laythe orbit. Try to do this from the Jool aerobrake to save fuel.
  
• Assess first mission’s status. Use rescue vehicle as required between Jool/Laythe SOI to save their sorry behinds.
  
• Recover two Kerbals from their swim meet somewhere in the Laythe ocean and rendezvous in orbit.
  
• Transfer to Vall
  
• Land, plant flag, return and dock, refuel at mother ship.
  
• Repeat for Tylo, Bop, and Pol.
  
• Return Kerbals to Kerbin.
  

Required equipment:

Based on the mission profile, I need to design a few different pieces.

• Laythe lander. Will need to be both land and sea capable as the splashdown point of the first mission’s base is unknown. Need 2800 m/s capability minimum to reach orbit but can save fuel on descent with parachutes. Crew capacity of four Kerbals on the possibility that the first mission’s ascent stage did not work, and four Kerbals are on the surface instead of the planned two.
  
• Boat thingy. I'm not sure where the first mission's base will land, but on the chance I can't get a decent pinpoint landing or if the first mission's ascent stage launches and splashes back down without reaching orbit, I'll need some sort of surface transport between the base and lander/ascent stage. Bonus points if I can make it a sea plane, because I'd like to explore Laythe by air.
  
• Tylo lander. This will need to be unique hardware, capable of 2500 m/s delta V at 1.5 TWR for landing and 2500 m/s at 1.5 TWR for takeoff. Need a fuel reserve for orbital rendezvous and docking. Single occupant.
  
• Vall, Bop, and Pol lander. Single stage, one-Kerbal lander. Ideally refueled at mother ship for reuse and mass savings. Plan for worst case Bop orbit of 950 m/s from the delta V map, so that’s 1900 m/s down and up, plus an allowance for piloting errors. Design for 2500 m/s to allow for maneuvering. Investigate possibility of doing Tylo landing first, and having the upper stage be the lander for the other moons.
  
• Rescue ship. Needs crew capacity of eight, seven if a lander stays on the mother ship during a rescue, to be able to rescue the entirety of the first mission’s crew if need be. Needs sufficient delta V to transfer between Jool and Laythe SOI, conduct rendezvous operations in an unknown inclination, and return to mother ship. Might be able to save fuel/burn time by using this as a ferry ship for the landers to/from the mother ship, which could stay in Laythe orbit. This can also serve as the main crew habitat for the whole mission, eliminating the need for crew capacity anywhere else.
  
• Interplanetary cruiser. Modular ship with docking ports for the above craft, plus enough fuel and engines to move the whole Shebang to Jool, between the moons, and return to Kerbin. The return to Kerbin is optional since the rescue ship could also probably add yet another function of a return craft if the delta V is high enough, and just use the cruiser as a refuel stop, but I'd like to be able to reuse the main ship if possible.
  
• Refuel tanker. Depending on what I get out of the above design process, they'll likely need some underway replenishment. The design of the ships (mass, TWR, and delta V) will determine how much fuel is needed for the return trip and operations in the Jool system. I'll have to design this last, but until then I'll make the planning assumption that I need to get two full Jumbo-64 tanks to Jool orbit.
  

Time to get to designing, and I'll add the vehicles as they develop.

[UH60guy]

I have now designed the boat thingy at 9.43 tons. This one was a good place to start as it didn't require any hard calculations- just something that can move over the water for a reasonable amount of time and fly to cover long distances even faster. This craft can make about 30-40 m/s in the water, and more in the air. It's able to takeoff and land in water and on land with a crew of two. I based it off the designs of Scott60UK's boatplane project, and it really seems to work well.

Now at 9.43 tons, the question this will raise will be how it is mounted to the mother ship. That will likely be enough to add in some asymmetric thrust problems, so I will either have to balance it or take two of these along. I'll also need some sort of reentry package attached so it can deorbit.

Edited October 3, 2013 by UH60guy

[UH60guy]

Jeb's Junkyard Jalopy Manufacturing Inc. is starting work on the Tylo lander next. They're employing the backwards planning process, so they will finalize the ascent portion before designing the landing portion of this vehicle.

Taking a look at the hard requirements will tell them what must be included, and then they can work on the "nice-to-haves."

Starting from the requirements:

1. Crew of 1 (mission to plant flag)
   
2. Docking port (for transport on mother ship and re-use)
   
3. Ascent stage delta V of 2500 m/s with 1.5 TWR minimum (would be nice to get home in time for dinner)
   
4. Attitude control- either RCS fuel/thrusters or torque/electricity
   
5. Landing legs, since this will be reused as a lander for the other moons (minimize risk of everything exploding by landing on an engine)
   
6. Means to reenter the spacecraft (low gravity of most moons could allow for a jump and grab, Tylo might require a ladder down past any lower stage)
   

Nice to haves:

1. MOAR BOOSTERS (more delta V for maneuvering)
   
2. Landing lights (though Jeb flies with his eyes closed anyway, this is purely for the photogtaphers' benefit)
   
3. RCS (much easier to dock)
   
4. Science package (thermometer and gravity measurement)
   

First iteration design is complete. It looks like a bacteriophage virus. Due to the requirement of a docking port, it was difficult to place an external command seat to save mass. Strapping one to the side... well... that didn't end well in testing due to imbalance. Instead, they went with a standard docking port on top and a Mk. 1 Lander Can immediately underneath.

This sits on top of a probe core for torque, and a FL-T400 fuel tank. The probe core is powered by a radially mounted RTG, since we expect to get some eclipses from Jool and solar power may be unreliable. They didn't have enough mass to spare to add any monopropellant and RCS while still meeting delta V and TWR requirements. Instead it will have to get close to the mother ship and have the other ship execute the docking maneuvers.

Three small Rockomax 24-77 engines are radially mounted. Original design used a LV-909, but using the three smaller engines further reduced mass and increased TWR, at the cost of total delta V.

A ladder comes down the side and can meet up with anything in the lower stage, or allow access to the ground.

For nice-to-haves, they can get on two flood lights before it goes below the 2500 m/s requirement. No science package included.

We'll try another design approach and have the vehicles compete against each other, but this one clocks in just above the 2500 m/s requirement at a TWR of 1.63 with full fuel.

Edited October 3, 2013 by UH60guy

[UH60guy]

Looks like Jeb was beaten out in the lander design competition.

Using a similar design, but replacing the Mk 1 Lander Can with a framework, allowed for significant mass savings. That allowed for the addition of science instruments and lights as well, but still no RCS.

The design chosen for the Tylo ascent stage clock in at a mass of 3.28 tons, with a 1.55 TWR and 3604 m/s delta V in a vacuum.

However, they did provide a RCS capable design- if the scientists determine a 1.39 TWR with 3002 m/s version can take off from Tylo, that's the version they'll use as the RCS capability will make things a lot easier.

Here is the RCS capable design. The only difference for the non-RCS version is the lack of RCS tank and thrusters.

The next step will be to build the lower stage to this craft, so that it can descend and land on Tylo. They'll need to add on another 2500 m/s capability with a planned TWR of 1.5. to get it down there. That part will be expendable and have minimal requirements since the upper stage seems to meet most of them already. This is where the backwards planning process really helps!

Edited October 4, 2013 by UH60guy

[UH60guy]

I really love the backwards planning process, since it makes it easier to design when you already have built the payload. The payload in this case is the ascent stage for the Tylo (and other moon) lander.

The requirements for this stage were:

Large docking port (1.5 meter docking ports and I aren't on speaking terms after some previous interplanetary mother ships' transfer burns went awry)

2500 m/s delta V at 1.5 TWR for just this stage

Landing legs (I plan on reserving all the upper stage's fuel for the ascent)

In the end, I came up with the below design. It has two LV-T30 engines radially mounted beside some large diameter fuel tanks in two stages. The lower stage has the large docking port and will be jettisoned during descent (the upper stage has a 1.5m docking port, but it's a low mass ship and should avoid wobbling when attached to the mother ship).

This design has 3726 m/s delta V available on the lower stage alone, with a minimum thrust/weight ratio of 1.68. That makes the total for the ship 6729 m/s, which means I can probably use remaining fuel on the landing stage to help out the ascent- mitigating the upper stage's 1.39 TWR and making the decision to include RCS a whole lot easier. I even had enough extra power and fuel to add a few aesthetic touches, like the jet housings and nose cones on the engines.

[UH60guy]

Next step was to build the Laythe lander and ascent module for four Kerbals. However, comparing that to the requirement for a 7 or 8 Kerbal capacity in the rescue ship, I think there's an efficiency to be gained here.

Why should I have two craft with a combined capacity of 12, when I can build two craft with some common parts for a combined capacity of 8?

I'll look at the mass savings, but right now I think hitchhiker containers are the best bet- at only 2.5 tons each, they have more capacity than both the Mk II command pod or the Mk 2. lander, at the same or less mass. That tidbit of information will let me make the rescue ship with two hitchhikers (for a crew compliment of 8), at less mass than a hitchhiker plus command module and a capacity of 7. Plus, the requirement for the Laythe lander to have a capicty of four also leads me to favoring use of a hitchhiker.

So, what does that tell me? The two craft should share a hitchhiker between them. That can be done with a hitchhiker pod built with a Clamp-o-tron Sr. on both ends. The Laythe lander can take it to the surface and back, then give it to the rescue ship to get its capacity to 8. The Laythe ascent stage can be jettisoned at that point, and we'll be left with a fully functional rescue ship/taxi. Plus, if the first mission goes exactly as planned, this mission will only require a crew capacity of 3- negating the need for the second hitchhiker on the rescue ship, which can then be jettisoned then for some mass savings and delta-V gain for puttering around in the Joolean system.

[UH60guy]

Wow, I step away for a few days for some family stuff, and 0.22 comes out and blows away my plans I think I'm going to indefinitely shelf this mission and start over on 0.22 in career mode. These spacecraft should be useful for future missions at least, but I think I'd like to focus on the progression aspect of career mode for a while. We'll see what other missions can be recovered from "out there" and I'll chalk it up to Jeb's crazed dream before his first launch in career mode.