Lowest Mass To Duna and Back Challenge

[Kergarin]

4 hours ago, sevenperforce said:

Question -- if one chooses the command pod version rather than the command seat version, must the pod itself land on Duna, or can you simply use a command seat for the landing and use a pod for the return?

Also, if you use a pod, is there a requirement that the pod itself land on Kerbin or can you bail out and chute down?

I hope at least the second is allowed  Else I would have to adjust it a little...

Edit: Also if the first is allowed, I would have to start over again to get an even lower weight. 

I land the pod on Duna, return and reenter in the pod on kerbin, and bail out a few hundred meters above the ground to glide down on the personal chute

Edited March 20, 2019 by Kergarin

[sevenperforce]

42 minutes ago, Kergarin said:

I hope at least the second is allowed  Else I would have to adjust it a little...

Edit: Also if the first is allowed, I would have to start over again to get an even lower weight. 

I land the pod on Duna, return and reenter in the pod on kerbin, and bail out a few hundred meters above the ground to glide down on the personal chute

My current version, that lands a capsule on Duna and then returns it to Kerbin by chute, is 6.004 tonnes. I have a version at 5.21 tonnes but can't quite make orbit at Kerbin. I found that using a chute-assisted propulsive landing at Duna took less mass than going pure propulsive, and since I had the chute anyway I might as well repack and use it at Kerbin. I suppose I could attach the chute to one of my ascender's drop tanks and thus save a bit of weight for the Duna LV and transfer stage, but I don't know it would save that much.

I assume you are, like me, using an ion transfer stage and leaving it in low Duna orbit, while using (primarily) biprop for the Duna ascent?

[Johnster_Space_Program]

1 hour ago, Kergarin said:

I hope at least the second is allowed  Else I would have to adjust it a little...

Edit: Also if the first is allowed, I would have to start over again to get an even lower weight. 

I land the pod on Duna, return and reenter in the pod on kerbin, and bail out a few hundred meters above the ground to glide down on the personal chute

for the command seat section, yes you can bail out and land with the kerbal parachute, that's what your supposed to do.

[Kergarin]

13 minutes ago, sevenperforce said:

My current version, that lands a capsule on Duna and then returns it to Kerbin by chute, is 6.004 tonnes. I have a version at 5.21 tonnes but can't quite make orbit at Kerbin. I found that using a chute-assisted propulsive landing at Duna took less mass than going pure propulsive, and since I had the chute anyway I might as well repack and use it at Kerbin. I suppose I could attach the chute to one of my ascender's drop tanks and thus save a bit of weight for the Duna LV and transfer stage, but I don't know it would save that much.

I assume you are, like me, using an ion transfer stage and leaving it in low Duna orbit, while using (primarily) biprop for the Duna ascent?

Yes exactly. Ion transfer stage and lf/ox lander. I do a chute assisted landing too, but then drop it before taking of from duna. 

Keeping the chute would just require some more xenon, which does not weight that much. But it would be a hell of work to redo it.  the video is cut since days... I'm just waiting for a friend to compose some music. Maybe I should do a preview without it until then.

Also: are wo allowed to repack chutes with pilots in sandbox?

I also tried landing a single stage with biprop and xenon, hoping I would require less heavy biprop and circularize on ions. Also saving some docking ports and maneuvering But this turned always out to be heavier.

Actually I'm using the mk1 pod, which is rather heavy but more aerodynamic (why in the world is Dunas thin atmosphere that draggy?). I had some concepts using the mk1 can at around theoretical 5.2t too, but it has horrible aerodynamics at launch on kerbin due to a massive fairing.

By leaving the pod in duna orbit, going down on a seat, I guess less than 5t would be possible.

[herbal space program]

29 minutes ago, sevenperforce said:

My current version, that lands a capsule on Duna and then returns it to Kerbin by chute, is 6.004 tonnes. I have a version at 5.21 tonnes but can't quite make orbit at Kerbin. I found that using a chute-assisted propulsive landing at Duna took less mass than going pure propulsive, and since I had the chute anyway I might as well repack and use it at Kerbin. I suppose I could attach the chute to one of my ascender's drop tanks and thus save a bit of weight for the Duna LV and transfer stage, but I don't know it would save that much.

I assume you are, like me, using an ion transfer stage and leaving it in low Duna orbit, while using (primarily) biprop for the Duna ascent?

I'm currently at just under 6.4t with something that should be able to do both Duna and Ike, landing the pod on both bodies and then Kerbin in the end. For me the breakthrough was twofold: 1) remembering that you can mount the ion engine directly behind another engine, and it still works the same. and 2) Figuring out that the Diverterless Supersonic Intake is total bunk. Not sure now why anybody would ever want to use that part.

Edited March 20, 2019 by herbal space program

[Kergarin]

7 minutes ago, Johnster_Space_Program said:

for the command seat section, yes you can bail out and land with the kerbal parachute, that's what your supposed to do.

But I'm using a mk1 pod for the tour. Is bailing out for the touchdown at Kerbin ok too? 

I have to say, I didn't think about this, as it felt legit, as the Kerbal is well protected and comfortably travelling in  the command pod during the entire trip.H e just jumps out at Kerbin in a height of around 1200m, where it is save and close to home 

If you say it's not legit, I will start over again

[Johnster_Space_Program]

18 minutes ago, Kergarin said:

But I'm using a mk1 pod for the tour. Is bailing out for the touchdown at Kerbin ok too? 

I have to say, I didn't think about this, as it felt legit, as the Kerbal is well protected and comfortably travelling in  the command pod during the entire trip.H e just jumps out at Kerbin in a height of around 1200m, where it is save and close to home 

If you say it's not legit, I will start over again

yes, it is.

[sevenperforce]

29 minutes ago, Johnster_Space_Program said:

for the command seat section, yes you can bail out and land with the kerbal parachute, that's what your supposed to do.

For a command pod version, can I leave the command pod in Duna orbit and use a seat for the lander? Or does the pod have to land on the surface of Duna to count?

30 minutes ago, Kergarin said:

Keeping the chute would just require some more xenon, which does not weight that much. But it would be a hell of work to redo it.  the video is cut since days... I'm just waiting for a friend to compose some music. Maybe I should do a preview without it until then.

Also: are wo allowed to repack chutes with pilots in sandbox?

I don't see why not.

30 minutes ago, Kergarin said:

I also tried landing a single stage with biprop and xenon, hoping I would require less heavy biprop and circularize on ions. Also saving some docking ports and maneuvering But this turned always out to be heavier.

I used monoprop and a single linear thruster for circularization of the module, since it contains its own monoprop reserves. 

30 minutes ago, Kergarin said:

Actually I'm using the mk1 pod, which is rather heavy but more aerodynamic (why in the world is Dunas thin atmosphere that draggy?). I had some concepts using the mk1 can at around theoretical 5.2t too, but it has horrible aerodynamics at launch on kerbin due to a massive fairing.

I'm using the mk1 can rather than the pod for mass reasons but aero problems are keeping me right around 6 tonnes.

[Kergarin]

32 minutes ago, herbal space program said:

I'm currently at just under 6.4t with something that should be able to do both Duna and Ike, landing the pod on both bodies and then Kerbin in the end. For me the breakthrough was twofold: 1) remembering that you can mount the ion engine directly behind another engine, and it still works the same. and 2) Figuring out that the Diverterless Supersonic Intake is total bunk. Not sure now why anybody would ever want to use that part.

Yes, this intake is bad at high speeds and worse at static. A better intake should give the rapier the power to launch without those sepratrons.

An inline mounted ion engine works indeed and makes things easier. But I personally don't do this, as it feels wrong to me. 

You could also think about getting rid of the wings, and go for a flat ballistic trajectory as I do.

[herbal space program]

6 minutes ago, Kergarin said:

Yes, this intake is bad at high speeds and worse at static. A better intake should give the rapier the power to launch without those sepratrons.

An inline mounted ion engine works indeed and makes things easier. But I personally don't do this, as it feels wrong to me. 

You could also think about getting rid of the wings, and go for a flat ballistic trajectory as I do.

Once I changed intakes and made it all into one stack, all my problems pretty much went away. This is what it looks like now:

 

As you can see, the wings and Sepratrons are long gone now, since it is now light and aerodynamic enough to scream into the sky without such help. Getting it to reach almost 1500 m/s on just the air-breathing Rapiers also allowed me to dispense with the extra Spark engine, reducing weight even more. This version has 4.2 km/s on orbit, with about 1300 of it on the Spark, so I believe it should be able to do Ike. A previous version with one less T100 tank still had enough to do Duna alone and came in around 5.8t. Anyway, I still don;t think I'll beat yours, but at least it's respectable!

[Kergarin]

5 minutes ago, herbal space program said:

Once I changed intakes and made it all into one stack, all my problems pretty much went away. This is what it looks like now:

...

As you can see, the wings and Sepratrons are long gone now, since it is now light and aerodynamic enough to scream into the sky without such help. Getting it to reach almost 1500 m/s on just the air-breathing Rapiers also allowed me to dispense with the extra Spark engine, reducing weight even more. This version has 4.2 km/s on orbit, with about 1300 of it on the Spark, so I believe it should be able to do Ike. A previous version with one less T100 tank still had enough to do Duna alone and came in around 5.8t. Anyway, I still don;t think I'll beat yours, but at least it's respectable!

It comes really close, only a few details in stages and so are different. 

I will be releasing a preview of mine in a few minutes.
There is still some small margin in my desing, by using less batteries and solar panels and tweaking fuel even more. But this would be pain to execute.

26 minutes ago, sevenperforce said:

 

I used monoprop and a single linear thruster for circularization of the module, since it contains its own monoprop reserves. 

I'm using the mk1 can rather than the pod for mass reasons but aero problems are keeping me right around 6 tonnes.

Is using nonprop efficient on your design? In most of my designs, the weight of just one linear thruster and nonoprop took more dv than it gave.

I also did not give up the can version. Still working on both to see how low we can push this.

[Kergarin]

That's what i got actually:

5.794 tons

 

that Ike Landing was absolutely unintended. 
I just realized how much dv i had left in Duna Orbit, and gave it a try.
 

Combining a Whiplash first stage with a Spark turned out to be more efficient than an rapier.
The solar panels are mounted asymetrical to always ensure all 4 can get into direct sunlight
 

 

 

Edited March 20, 2019 by Kergarin

[sevenperforce]

48 minutes ago, Kergarin said:

Is using nonprop efficient on your design? In most of my designs, the weight of just one linear thruster and nonoprop took more dv than it gave.

I suppose I could loft the can without any monoprop in it, but it seems a waste to leave that capacity untapped.

13 minutes ago, Kergarin said:

 

Combining a Whiplash first stage with a Spark turned out to be more efficient than an rapier.

I also converged to a Whiplash+Spark combo rather than a Rapier, but I managed to use the same spark for Duna ascent that I used for Kerbin. Gotta love those roundified tanks. I think my problem remains aerodynamics during Kerbin ascent.

[Kergarin]

1 hour ago, sevenperforce said:

I suppose I could loft the can without any monoprop in it, but it seems a waste to leave that capacity untapped.

I also converged to a Whiplash+Spark combo rather than a Rapier, but I managed to use the same spark for Duna ascent that I used for Kerbin. Gotta love those roundified tanks. I think my problem remains aerodynamics during Kerbin ascent.

That's also an interesting idea. What's your landers weight wenn starting the descend to dunas surface?

[sevenperforce]

1 hour ago, Kergarin said:

That's also an interesting idea. What's your landers weight wenn starting the descend to dunas surface?

I'll have to go back to that model and look it up later. IIRC, though, it was:

• Lander can full of monoprop
• Single linear RCS thruster
• Two small solar panels
• Cubic strut and small chute
• Docking port jr
• Two tiny-sized decouplers
• Smallest 1.25m tank
• Spark
• Roundified prop tank

[jinnantonix]

Kergarin wrote

Quote

That's what i got actually:

5.794 tons

Too good.  I spent 4 hours today testing designs.  I kept coming back to your solution.

[Kergarin]

9 hours ago, sevenperforce said:

I'll have to go back to that model and look it up later. IIRC, though, it was:

• Lander can full of monoprop
• Single linear RCS thruster
• Two small solar panels
• Cubic strut and small chute
• Docking port jr
• Two tiny-sized decouplers
• Smallest 1.25m tank
• Spark
• Roundified prop tank

My pod lander is 1.705t wet and with chute, and 0.82t after decoupling chute, engine and fueltanks. 

Your can seems to be around 1.6t. my cans also ended up in this area. But the problem I'm facing besides the fairings drag is the fairings weight. I need around 0.2t extra fairing to cover it, ending up actually heavier at launch.

We save a little xenon for the transfers and Ike landing, but that would be less than 0.01t.

But I'm still trying to optimize both.

 

Question: what about making history parts?

 

 

2 hours ago, jinnantonix said:

Kergarin wrote

Too good.  I spent 4 hours today testing designs.  I kept coming back to your solution.

Thanks! Yes, also my other solutions all perform worse.

Edited March 21, 2019 by Kergarin

[sevenperforce]

41 minutes ago, Kergarin said:

Your can seems to be around 1.6t. my cans also ended up in this area. But the problem I'm facing besides the fairings drag is the fairings weight. I need around 0.2t extra fairing to cover it, ending up actually heavier at launch.

We save a little xenon for the transfers and Ike landing, but that would be less than 0.01t.

 

Fairing is killer. I have my transfer stage mounted on top of my capsule, to allow my Duna landing spark to do its thing from the time the Whiplash separates, and so my fairing is really long.

41 minutes ago, Kergarin said:

Question: what about making history parts?

I have tried the Vostok-style capsules but their fairing problem is as bad as the lander can's, and you need to add a reaction wheel anyway.

Some of the tanks could prove useful though.

41 minutes ago, Kergarin said:

Also my other solutions all perform worse.

Playing around with a Juno-based first stage but no luck so far.

[GRS]

@Kergarin, not bad for some old man with little tech time, wish i'm as good as you in small stuff like that...

[Kergarin]

37 minutes ago, sevenperforce said:

...

Playing around with a Juno-based first stage but no luck so far.

The panther could also be interesting. That's still on my list.

I'm playing around with your monoprop idea on the pod, but still ending up heavier. (I won't post this as my entry, if it succeeds, since it's your idea)

The can always runs into some barrier around 200-240m/s in dunas atmosphere, where drag becomes bigger than thrust, while the pod blasts throug it with 500 and still accelerates.

Actually I'm trying smaller engines on the lander, the Spark is heavy and gives a twr >4 which is not really needed.

11 minutes ago, GRS said:

@Kergarin, not bad for some old man with little tech time, wish i'm as good as you in small stuff like that...

Thanks  actually I'm on holiday, so I can spend a little more time 

They key in small things is picking the right engines. Most just use too heavy ones. U usually have to pick an engine one diameter smaller than the ship for medium g landers and transfer stages.

For example the Terrier seems to be the right choice for 1,25m rockets, as it's the correct size and has a verry good ISP. 

But that's wrong. It is 5 times as heavy as the Spark and 25 times heavier than the spider. Especially the Spark has a verry good twr and can lift much heavier payloads than expected.

 

[sevenperforce]

1 hour ago, Kergarin said:

I'm playing around with your monoprop idea on the pod, but still ending up heavier. (I won't post this as my entry, if it succeeds, since it's your idea)

The can always runs into some barrier around 200-240m/s in dunas atmosphere, where drag becomes bigger than thrust, while the pod blasts throug it with 500 and still accelerates.

Actually I'm trying smaller engines on the lander, the Spark is heavy and gives a twr >4 which is not really needed.

I tried clustering Ants because they have higher Isp than the Spiders but ended up with a really anemic TWR. That approach did allow for parallel mounting, though, which meant I could use the monoprop in parallel and add mono drop tanks. I may revisit.

[Kergarin]

2 minutes ago, sevenperforce said:

I tried clustering Ants because they have higher Isp than the Spiders but ended up with a really anemic TWR. That approach did allow for parallel mounting, though, which meant I could use the monoprop in parallel and add mono drop tanks. I may revisit.

I'm actually working on onion and asparagus staging using ants and spiders. Looks verry promising until now. Might squeeze out 0.1t

[sevenperforce]

4 minutes ago, Kergarin said:

I'm actually working on onion and asparagus staging using ants and spiders. Looks verry promising until now. Might squeeze out 0.1t

I need to test SL thrust of ant and spider on Duna. I can't remember the scale height curve so I am just doing it manually. If Ants can be used then it's huge for terminal Isp....

[sevenperforce]

Just tested and at 660 m over Dunian SL the Ant already has a higher Isp than the Spider, so there's no reason to use a Spider. Paradoxically, the Spider has a slightly higher TWR ratio at SL because it is closer to its maximum Isp than the Ant, but it's a negligible difference.

[Kergarin]

34 minutes ago, sevenperforce said:

Just tested and at 660 m over Dunian SL the Ant already has a higher Isp than the Spider, so there's no reason to use a Spider. Paradoxically, the Spider has a slightly higher TWR ratio at SL because it is closer to its maximum Isp than the Ant, but it's a negligible difference.

That's true, dunas thin atmosphere is almost like vacuom, even at the ground.

Besides from this, I think we are coming to that point where we have to figure out dunas highest equatorial mountain, to minimize the drag problems.