What would be a good approximate design for this probe?

[CaptainApollo]

Hello! I am hoping to send a probe to Dun which will not come back to Kerbin, it will be a one-way trip and it will only land there and transmit the science collected. I was wondering what would be a good approximate design, I would just like more of a guideline. Thank you!

[Slam_Jones]

Well, are you playing Career or Sandbox? The level of tech available to you makes a huge difference

Edit: Generally, however, I'd do something like this:

Probe stage: (what will actually land on Duna)

Smallest probe core available

RTG for nighttime charging (I tend to clip them directly into the center of something)

Small battery for backup, and so you can transmit data without interruption (enough so you can transmit your biggest data transmission without it running out of charge)

Science stuff

Transmitter

Parachute (I haven't landed on Duna in a while, so multiple may be required)

Small booster with limited fuel to help slow down, if needed (depends on weight of probe and effectiveness of chute)

Landing legs (3 of the tiny ones should be enough)

Transfer stage: (to get you from LKO to Duna)

Xenon container

Ion thruster

Solar panels enough to power said thruster

Extra battery

Airbrakes for initial aerobraking (I usually play at 0% re-entry heat, so if this doesn't work with the heat enabled, just skip it)

- This stage would be dropped once you've slowed down enough

Any stages below this should be chemical rockets with enough oomph to get you to LKO, minimum. Or, if you're brave, send it up in a Spaceplane

Edited September 11, 2015 by Slam_Jones

[ForScience6686]

I just sent my first probes, and my advice is to stay small. I broke it up into two probes, one for a polar orbit and to scan for resources, the second a tiny rover that will be dropped by sky crane. The main purpose of this mission is to locate a suitable mining location for future manned missions which I'm planning for now. But they both include a full array of science gear. Keeping everything light makes everything much easier, I went through 3 design changes that focused on minimalist designs.

[Gaarst]

Probe core, landing legs, batteries (a few hundred units is OK for transmitting most stuff), solar panels (deployed after reentry and landing !), RTG if not in career mode, science experiments, antenna and that should be it.

For landing: parachutes, and rockets for if parachutes do not slow it down enough (powered landing).

Encase the whole thing in a fairing + heatshield which will be used for reentry and ejected before landing. You may not need them, but it's safer that way.

The total mass of this should be 1-1.5t if you don't put hundreds of each parts.

I think that's it for your landing probe, good luck with your landing !

Disclaimer: I am not responsible for any critical failure due to essential equipement missing...

[CaptainApollo]

Thank you, your ideas seem quite good! And it is career, if it was sandbox I'd just slap something together. And any ideas for the rocket?

[Slam_Jones]

If it's as light as I think it is, you could prolly pop a decoupler, fl-T400 tank, and a Terrier for the upper stage, and then a decoupler, two FL-T800 (or one FL-T800 and one FL-T400) tanks and a Reliant or Swivel and that should get it to orbit. If that's not enough, put two radial decouplers with the smaller SRB's on them. Launch in tandem with main engine, drop when fire stops coming out.

[CaptainApollo]

Thank you, that sounds very good, I am now as ready as I'll ever be!

[Slam_Jones]

It may take a couple attempts to get it right (I know it did for me) but once you do it's a pretty awesome feeling

Good luck!

One last tip: because the atmo is so thin, aerobraking won't do nearly as much as it does on Kerbin, so you gotta really be ready for it. Chutes also won't do as much, so a drogue chute plus a regular chute might be a good combo.

[GoSlash27]

for 1.5t payload to Duna? Lemme see...

Assuming you want a low tech solution, you're looking at a 20t launcher so you'll need a pad upgrade.

Stage 1 (boost)

2 LV-T30s with 2 stacks of FL-T800+FL-T200

or

3 Mk.55s with 2 FL-T800s and 1 FL-T400

or

a Skipper, 1 X200-16 and 1 X200-8

Stage 2 (orbit)

LV-909, an FL-T400 and an FL-T200

Stage 3 (Duna)

48-7S and an FL-T200

Best,

-Slashy

[ForScience6686]

It may take a couple attempts to get it right (I know it did for me) but once you do it's a pretty awesome feeling

Good luck!

One last tip: because the atmo is so thin, aerobraking won't do nearly as much as it does on Kerbin, so you gotta really be ready for it. Chutes also won't do as much, so a drogue chute plus a regular chute might be a good combo.

This is why I'm going with the sky crane for a powered decent after drogue chute release. The chutes are only there (I hope) to maintain orientation as it comes down.

[Snark]

I find that a partially-powered landing works best for Duna; trying to land using parachutes only is doable, but you need to use so many chutes that it's actually quite a bit less mass to use a small fuel tank and engine instead.

Good design for a small Duna lander that doesn't need to take off again:

Mk16 chute

Oscar tank

Spark engine

HECS core

Some OX-STAT panels, tilted up a bit

Science instruments

Batteries

Antenna

...in other words, pretty much what Slam_Jones said. I tend to favor having ~4-6 OX-STATs instead of an RTG (less mass, available lower in tech tree, can help hold probe upright if they're properly placed), and I generally skip the landing legs (saves a little mass, and if I'm not taking off again, I don't care as much whether the probe tips over on landing).

Use the engine to slow down to under 250 m/s as you near the surface. Pop the chute and let it slow you down to terminal velocity, drifting down to the surface. Use a brief engine burst to slow down to a safe speed just before landing.

As for the rest of the rocket: that's fairly straightforward. Bear in mind that a well-timed Duna mission needs only slightly more dV than a Mun mission, so you can use pretty much the same design for the booster and transfer stages.

Edited September 13, 2015 by Snark