ft800 / terrier upper stage enough for a mun mission

[AeroGav]

Hey guys,

In my latest career game I just got a contract to go to the Mun.  It will be the first celestial body I actually landed on in this game, which is a bit of a departure as every other career game I go straight to Minmus.  In fact I might have only been to the Mun once and that was sandbox.

The problem is my tech level atm is Terrier, FT800 and Panther only.  My best launcher can put a full ft800 and terrier in low kerbin orbit, but is that enough to get to the mun and back?

If not, was thinking to send two vehicles,  one with the science stuff + landing legs, that flies to mun, lands, jettisons the science gear, takes off to mun orbit.   The return ship has re-entry stuff and parks in munar orbit waiting for the brave kerbonaut to EVA across.    That architecture might work out if the single launch just falls short, since we're not saving much delta V (with aerobraking, low munar back to Kerbin is the easiest part of the mission, but perhaps the heat shield/chute/radiator mass left off the outbound stage will help.

BTW  when i say "best launcher", this is a "no rockets" challenge.    It's a disposable panther/terrier spaceplane, that jettisons every single part of itself, that puts the upper stage in orbit ! 

[bewing]

It's certainly enough to get to high Munar orbit, but it's not enough to get landed and back up again -- need an extra 1100 dV for that, and I don't think you have it. Probably best to go back to Minmus, truly.

It's easy to test in the sandbox, though.

-- Although, adding a klaw so that you can refuel would certainly be enough to make it work.

Edited July 4, 2016 by bewing

[Reactordrone]

As long as it's not carrying a load of extra mass it should get there and back ok. If the wet mass/ dry mass is about 2.3 or more it has enough delta-v, given reasonable piloting.

[Snark]

1 hour ago, Reactordrone said:

As long as it's not carrying a load of extra mass it should get there and back ok. If the wet mass/ dry mass is about 2.3 or more it has enough delta-v, given reasonable piloting.

^ This.

Just to put some numbers on it:   Let's say your ship is around 6.5 tons in LKO.  (That allows for a full FL-T800, Terrier, Mk1 pod, and a half-ton or so of miscellaneous paraphernalia.)  That'll give you about 3200 m/s of dV.

That should be enough to get you to a Mun landing and back.  The main thing is to make sure you do it efficiently.  The main gotchas to watch out for:

• Make optimum use of Oberth effect on arrival.  You want your Pe over the Mun to be as low as possible (say, 10 km or thereabouts) and do your capture burn there.
• Do a properly-executed suicide burn to land.
• Efficient takeoff from the Mun:  crank it over to nearly horizontal the moment you lift off, and accelerate mostly-horizontally to a very low Mun orbit.
• Efficient burn to get home: eject from very low circular Mun orbit for maximum Oberth benefit.

The dV budget will be enough to do the above with a reasonable safety margin.  It does not include much budget for slowing down before hitting Kerbin atmosphere upon return, so a heat shield would be a good idea (doesn't need much ablator, even just 20% will be plenty).

[Streetwind]

Guys, don't encourage him. This is a bad idea.

Even if he had enough dV - trying to land a pod+fl-t800+terrier stack upright on the Mun is a foolhardy endeavour. Any slope at all, and it will topple. And since he wants to go back to Kerbin, landing horizontally is out of the question... He also isn't talking about how to supply power. If his highest tech is the node with the Terrier in it, he probably doesn't have solar panels. That may make the mission heavier than usual.

My recommendation? Build a better lifter, and push a proper Mun lander into orbit. If necessary, do a polar orbit around Kerbin and farm some EVA reports for science so you can unlock struts (but I wouldn't consider it strictly necessary).

 

EDIT:

@AeroGav , if you can lift 8.1 tons to LKO, this should have you covered for a low tech Mun lander:

0.1000 - parachute
0.8000 - pod (no monoprop)
0.2000 - heatshield (half ablator)
0.0500 - decoupler
0.5625 - fl-t100
0.5000 - terrier
---------------
2.2125 - return stage (866 m/s)


2.2125 - return stage
0.0500 - decoupler
0.2000 - materials bay
0.0050 - z-100 battery, radially attached to materials bay
0.0050 - z-100 battery, radially attached to materials bay
0.0100 - thermometer, radially attached to materials bay
0.0500 - mystery goo, radially attached to materials bay
2.2500 - fl-t400, radially attached to materials bay
2.2500 - fl-t400, radially attached to materials bay
0.0150 - micro landing strut, radially attached to fl-t400
0.0150 - micro landing strut, radially attached to fl-t400
0.0150 - micro landing strut, radially attached to fl-t400
0.0150 - micro landing strut, radially attached to fl-t400
0.5000 - terrier, attached to fl-t400
0.5000 - terrier, attached to fl-t400
----------------
8.0925 - transfer and landing stage (2306 m/s)

Try to balance the mystery goo with the two batteries and the thermometer. Not perfect, but it'll help.

And yes, it's kind of a sin against aerodynamics... you can probably put nosecones onto the radial tanks, now that I think of it, but in my experience such things launch fine anyways. Especially if you have a reasonably beefy lifter underneath it. Remember, you want to put this in orbit without consuming any of its fuel.

Mission profile:
- Sloppy 900 m/s Mun transfer with room for a correction burn to lower PE before entering Mun SOI, plus 550 m/s Mun orbital velocity, leaves 856 m/s for circularizing at 10 km and gravity losses during landing. Should be plenty.
- When encountering a slope, orient your lander lengthwise (radial tanks facing down and up the slope, not perpendicular to it).
- Make sure you pick up all the science reports and put them into your pod, because the instruments are not coming home.
- You might want to lock the electric charge on the pod until it is time to return to Kerbin, so it is still full by that time. Just don't forget to unlock it before takeoff.
- 550 m/s Mun orbital velocity and 250 m/s ejection burn to direct Kerbin reentry leaves 166 m/s buffer in the return stage, plus whatever you managed to save while landing.
- 30 km Kerbin periapsis should put you down on the surface in one go, without burning you up.

Edited July 4, 2016 by Streetwind

[Snark]

8 hours ago, Streetwind said:

Guys, don't encourage him. This is a bad idea.

Even if he had enough dV - trying to land a pod+fl-t800+terrier stack upright on the Mun is a foolhardy endeavour. Any slope at all, and it will topple.

Sure, it'll be dicey.  However, it's doable (I've landed contraptions like that).

It's certainly not optimal... but if he's working at a low tech level, and is running under some self-imposed house rules that require it to be part of an air-breathing SSTO, it might fit his conditions.  Hard to say, without screenshots or a more detailed explanation of exactly what the "house rules" are.

Personally, I find that the sweet spot with the Terrier is the 2-ton LFO tank.  A Mk1 pod, 2-ton LFO, and Terrier makes an incredibly versatile vehicle, packing lots of dV and a decent TWR into a small, lightweight package that can sit on top of just about anything.  I use it all the time, even in late career when I have the whole tech tree unlocked.

[AeroGav]

5 hours ago, Snark said:

Sure, it'll be dicey.  However, it's doable (I've landed contraptions like that).

It's certainly not optimal... but if he's working at a low tech level, and is running under some self-imposed house rules that require it to be part of an air-breathing SSTO, it might fit his conditions.  Hard to say, without screenshots or a more detailed explanation of exactly what the "house rules" are.

Personally, I find that the sweet spot with the Terrier is the 2-ton LFO tank.  A Mk1 pod, 2-ton LFO, and Terrier makes an incredibly versatile vehicle, packing lots of dV and a decent TWR into a small, lightweight package that can sit on top of just about anything.  I use it all the time, even in late career when I have the whole tech tree unlocked.

I can't play for another 3 days due to work stuff,  but this is what I'd come up with so far to be my "Saturn V".   

It certainly looks Kerbal enough...

the jet engines fall off , the aerodynamic surfaces attach to the front FT800 tank which is discarded in low orbit.   I can probably improve performance a bit more by Asaparagus staging the two side mounted terriers.

I'm a passable airplane flyer but not at all confident in orbital manuvers, suicide burns etc so i'll do what i can to help myself by making the return stage a separate vehicle.  I'll launch that first, unmanned, and leave it in munar orbit.   Jeb can eva over after returning from the surface.  Slightly lowers the delta V requirement of each vehicle.

Streetwind  does have me worried about the topple problem. I could use two 400 capacity tanks instead of one ft800, put a stack separator on, by the time i begin my final descent i'll be down to less than half fuel, throw away one of the tanks which will reduce the stack height some.  Maybe not jettison all my aero surfaces, a cruciform tail will help it balance better than a set of landing legs?

[Snark]

4 hours ago, AeroGav said:

I'm a passable airplane flyer but not at all confident in orbital manuvers, suicide burns etc so i'll do what i can to help myself by making the return stage a separate vehicle.  I'll launch that first, unmanned, and leave it in munar orbit.   Jeb can eva over after returning from the surface.  Slightly lowers the delta V requirement of each vehicle.

That'll make it a bit easier, yes.

Suicide burns don't really take a huge amount of practice-- it's just a question of tools & technique.  You can go for a "high-touch" mod like MechJeb that does the whole landing for you; a "low-touch" mod like BetterBurnTime that doesn't actually do anything for you, but does give you accurate time-to-impact and time-to-burn numbers so you can control with more confidence; or, if you prefer pure stock, you can use the maneuver-node trick to do pretty well.

(The maneuver-node trick:  Put yourself on a suborbital trajectory.  Drop a maneuver node right precisely at the point where your trajectory intersects the surface.  Grab the node's retrograde handle and pull on it until the trajectory collapses to a point and the prograde/retrograde handles start flipping back and forth.  There, you're all set.  The time-until-maneuver is how long you have until impact.  The estimated burn time is how long it will take you to come to a halt. Set your navball to surface mode, and set SAS to "hold retrograde".  Start your burn when the time-until-maneuver is around 60-70% of the estimated burn time.  Works like a charm.)

4 hours ago, AeroGav said:

Streetwind  does have me worried about the topple problem. I could use two 400 capacity tanks instead of one ft800, put a stack separator on, by the time i begin my final descent i'll be down to less than half fuel, throw away one of the tanks which will reduce the stack height some.  Maybe not jettison all my aero surfaces, a cruciform tail will help it balance better than a set of landing legs?

I prefer the landing legs myself, though I suppose a cruciform tail could work.

One way to make it a little steadier:  Do you have the Oscar tank unlocked yet?  You could reduce your 4-ton LFO tank to a 2-ton tank, then put four stacks of two Oscars each attached radially around the main tank.  Stick the 0.625m nosecone on the top/bottom of each Oscar stack to make it more aerodynamic during launch.  Then you can attach your landing legs (or cruciform tail) to the Oscars instead of the central tank.

That will make your ship both shorter and wider, and therefore considerably more tip-resistant.  You don't need to waste any mass adding fuel ducts:  just transfer fuel manually from the Oscars into the central tank as needed.

 

[AeroGav]

Well,   after a bout of food poisoning I finally did it :

The first pic in my previous post showed the vehicle intact on the runway, including 4 jet engines.   The second pic showed it having just dropped the jets, but with two underwing Terrier boosters.    The above pic is just after these have gone, with only the core engine remaining.

 

Front FT800 empty, it's time to ditch the airframe.   The launch exceeded expectations, I had planned to be at this point in low orbit, but actually our AP is up at 1,200km.  Notice the reported delta V goes up from 2700 to 3100 due to the loss of mass.  At this point,  I realised a major mistake.  What's Bill doing there?  The ship has an OCTO core so a non pilot can fly it, I had planned to bring a scientist so we could get multiple uses from our Science Jnr  and Goo experiments.   Well, it's a bit late for turning back I guess.

The lander stage has an ft400 and two ft200 tanks.   Because we got so much delta V out of the launcher,  we're late emptying the FT4.

My landing wastes a fair bit of fuel - it makes Neil Armstrong's look like a suicide burn. Even so we don't empty the top ft200 before touchdown, so we're taller than planned on the surface.   Despite that, the craft proves stable, even after Bill blunders into one of the landing legs and destroys it.

I'd planned to separate the Science Jnr before takeoff, but due to the staging order it wasn't possible to get rid of it before the final jettisonable ft200, by which point we're already sub-orbital.  I face retrograde before giving these items their Viking funeral, in the hope of extracting a little extra delta V from the explosion.  With over 1200dV however...

 

We didn't in fact have any need to make a separate return vehicle, in the end.   There was more than enough to get into a stable orbit, then escape from the Mun, and then could easily have brought our Periapse below 70km to aerobrake back to Kerbin.   Nevertheless I decide to stick to the plan and use our remaining fuel to get into a circular 300km orbit, which is low enough to minimize the delta V requirement of the crew retriever,  but high enough to allow high degrees of time warp while waiting for the rendez vous encounter.   Above pic shows Bill EVA'ing across to the return vehicle.   The munar lander will remain in high orbit as a permanent monument to this historic mission.

Edited July 9, 2016 by AeroGav
word repetition