Delta V for Duna Takeoff, Atmosphere important?

[davidpsummers]

I'm planning my first manned mission to Duna. Unlike the places I've been, it has an atmosphere. The delta-v map says it take 1380 m/s to reach low orbit. How close am I likely to get to that taking off through the atmosphere?

Edited July 31, 2014 by davidpsummers

[Champ]

I'm planning my first manned mission to Duna. Unlike the places I've been, it has an atmosphere. The delta-v map says it take 1380 m/s to reach low orbit. How close am I likely to get to that taking off through the atmosphere?

Values In dv map are calculated with the atmosphère. You should be able to reach orbit with less than 1500m/s.

Landing takes far less than that with chutes. Just dont Forget to repack them when landed.

[Laie]

Most Delta-V maps I know also take the atmosphere into account. If you map says 4500m/s for Kerbin, the 1380 for Duna are with atmosphere.

[Red Iron Crown]

Adding a safety cushion of about 10% should give a bit of leeway for a non-optimal ascent, so Champ's figure of 1500m/s is a good target.

Duna's atmosphere is so thin it can be virtually ignored during ascent. Unlikely that you'll hit or exceed terminal velocity unless you have an absurdly high TWR.

Good luck on your mission, Duna is a beautiful planet that I'm sure you'll enjoy visiting.

[biohazard15]

Landing takes far less than that with chutes. Just dont Forget to repack them when landed.

Although you most likely will need to use engines for final braking (or pack many chutes), Duna atmosphere is too thin for chutes alone to slow a good Duna lander\orbiter down to safe landing speed.

[Geschosskopf]

Just dont Forget to repack them when landed.

A note on repacking chutes.... Once you use a parachute in the normal staging sequence (via the spacebar), it doesn't always (or ever) work correctly again after repacking. I heard some rumors this might have changed in 0.24, or if you use the RealChute mod, but until I have a lot more confirmation I'm not going to trust them.

HOWEVER, there's a work-around that I know works so that's what I do. NEVER deploy chutes with the spacebar. Instead, put that on an action group. I have used this method many time and never had repacked chutes fail.

Also note: If you use RealChute, be sure to set the number of spare chutes to whatever you need. In stock, you have an infinite number of spares but in RealChute it defaults to 5 although you can change this.

Although you most likely will need to use engines for final braking (or pack many chutes), Duna atmosphere is too thin for chutes alone to slow a good Duna lander\orbiter down to safe landing speed.

It depends as you say on the number of chutes carried. Or if you use RealChute, you can use fewer bigger ones. It also depends VERY MUCH on the altitude of your landing site. Duna's air is so thin that a difference of a few hundred to a thousand meters of ground height makes a huge difference. There are a few depressions on Duna that have altitudes of 0-1000m. However, about 80% of the surface is endless dune fields that average 2000-3000m. A lander chuted to land in a depression will splat out in the dunes so it's vital to design the thing for a specific landing zone and be sure you hit it .

And hitting your LZ depends a lot on your descent profile. It's a lot easier to hit a specific point if you come down steeply, but that minimizes your passage through the air so your chutes have less time to work. OTOH, if you come in shallow, your chutes can do a lot better job for you, but then landing within 2-3km of your intended target is about the best you can hope for (although this is usually good enough unless you're trying to dock with something on the ground). Personally, I favor the low, shallow descent. Start from a 50km orbit, deorbit burn about 1/4 of an orbit away, and drop your trajectory about a finger's width east of your LZ.

Also note: If you're using stock chutes on Duna, be SURE to tweak their values. You want them to streamer at very high altitude, like 15km, and you want them to open fully about 4km (if landing in the dunes), a little less if landing in a depression. If you're using RealChute, it has its own calculator in it but be sure to set it for Duna because it defaults to Kerbin .

[EdFred]

Although you most likely will need to use engines for final braking (or pack many chutes), Duna atmosphere is too thin for chutes alone to slow a good Duna lander\orbiter down to safe landing speed.

Only if you over build. One should not have a problem landing chutes only on Duna. If you do, you're building it 'wrong.'

[davidpsummers]

Values In dv map are calculated with the atmosphère. You should be able to reach orbit with less than 1500m/s.

Landing takes far less than that with chutes. Just dont Forget to repack them when landed.

Well, I won't need the chutes after I land on this first mission. But how do you repack them?

[davidpsummers]

Yeah, I try to be careful with my Kerbals (I've stranded them but not killed any). 1500 m/s vs. 1380 is well within the margin I was allowing.

And thanks for the "Bon Voyage"!

[davidpsummers]

Although you most likely will need to use engines for final braking (or pack many chutes), Duna atmosphere is too thin for chutes alone to slow a good Duna lander\orbiter down to safe landing speed.

Yeah, I won't try landing on chutes alone. My experience with my unmanned landers was that you put a bunch in than fire engines real quick just as you touch down.

[davidpsummers]

And hitting your LZ depends a lot on your descent profile. It's a lot easier to hit a specific point if you come down steeply, but that minimizes your passage through the air so your chutes have less time to work. OTOH, if you come in shallow, your chutes can do a lot better job for you, but then landing within 2-3km of your intended target is about the best you can hope for (although this is usually good enough unless you're trying to dock with something on the ground). Personally, I favor the low, shallow descent. Start from a 50km orbit, deorbit burn about 1/4 of an orbit away, and drop your trajectory about a finger's width east of your LZ.

Also note: If you're using stock chutes on Duna, be SURE to tweak their values. You want them to streamer at very high altitude, like 15km, and you want them to open fully about 4km (if landing in the dunes), a little less if landing in a depression. If you're using RealChute, it has its own calculator in it but be sure to set it for Duna because it defaults to Kerbin .

My default is shallow. But I'm thinking of sending a rover on a separate vessel and if I do that, I will need to land it near the kerbalnauts. I've been assuming that even with a steep decent, I can use the chutes (thought maybe I'll do shallow for the Kerbals and then steep with the unmanned lander to be close without killing anyone :-).

Thanks for the comment about fully opening them early, that is good. I'm not sure what "streamer" means. There is that minimum pressure setting, but I was never sure what it was for. I clearly isn't when the open fully and I assume they come out when deploy them? (Currently, for Duna, I tend to deploy them just after the heating phase of aerobraking stops).

[metaphor]

Drogue chutes are really useful when landing on Duna, so that the main chutes don't break off on deployment.

[davidpsummers]

Drogue chutes are really useful when landing on Duna, so that the main chutes don't break off on deployment.

My main problem is that I have a docking port on top and I don't think there are side drogue chutes?

[Red Iron Crown]

My main problem is that I have a docking port on top and I don't think there are side drogue chutes?

Use the Radial Attachment Point thing to mount them.

[EdFred]

Use the Radial Attachment Point thing to mount them.

Or my favorite - structural girder with the drogue chute on the end of it. Which also allows for radial chutes to go on the girder. Three of those welded to the side of a lander help immensely.

[Pecan]

Only if you over build. One should not have a problem landing chutes only on Duna. If you do, you're building it 'wrong.'

NOW you tell me :-(

There I was, happily desiging and building for powered landings that are parachute-assisted just to save some dV, because I need the engines anyway and don't want extra chute mass. Anyway, now you've told me I'm doing it 'wrong' I'll change the way I play ^^. Remember folks, there are several criteria you may choose to optimise: mass, cost, part-count, ease of use ... or explosions.

(I'm not being entirely serious as I assume you aren't either, which is why you put 'wrong' in quotes).

[Pecan]

A note on repacking chutes.... Once you use a parachute in the normal staging sequence (via the spacebar), it doesn't always (or ever) work correctly again after repacking .... NEVER deploy chutes with the spacebar. Instead, put that on an action group.

Repacked chutes will work with action groups, even after initially being staged. It's the staging itself that only works once so, yeah, it's best to just forget about it and always use an action group.

[PS: What's with the 'spare' chutes? You're repacking them, so what do you need spares for?]

[EdFred]

Exactly. There are plenty of different ways to play. I often return to Kerbin with no chutes. As long as I have a TWR of about 3:1 and 300 or so dV remaining. But that's also at the end of my flight. I'm pretty sure the chutes are lighter than the extra fuel needed to retro burn to safely land on Duna - although I haven't done the numbers. I prefer chutes, and unlike stated previously in the thread you can land on Duna using zero engine burn (other than the little needed to initially reduce PE)

[allmhuran]

If you want to land on Duna using chutes alone you probably don't want to go from your solar orbit into encounter and then directly into aerobrake and landing, because Duna's atmosphere generally won't wash off all of that speed in one pass.

What you can do instead is first perform an aerocapture, and then perform multiple aerobraking passes to circularize your orbit more and more before coming in for your final aerobrake and landing.

[Pecan]

LOL - I wish I could directly aerobrake and land from encounter with any sort of precision, but I always circularise first so I can take my time picking my landing site.