Orbit & Return in How Little?...

[GarrisonChisholm]

Hey there. If one was to attempt a full science (all the basics plus the Materials Bay) probe to Eve or Duna that would Return to Kerbin Orbit without refueling, what is the least massive mission that is practical? My first attempt is (I am sure) embarrassingly large, and I'm wondering what the lightest anyone has ever managed it is.

[Superfluous J]

Orbit of Kerbin or landing on Kerbin? Also, I assume you want to flyby Eve or Duna, and not land?

I'd go with quite small. Probe core, science, heat shield (semi-optional), and enough fuel for say 2000-2500m/s. Burn at the right time to leave Kerbin and fly by the world (which will be like 1100m/s) and then back at your Sun apoapsis (after the flyby) burn whatever you need to return to Kerbin. If you're good, you can burn at Kerbin and aerobrake a bit to achieve orbit.

This probe will be surprisingly small, so the lifter to lift it should be similarly small. I'm not running the game now but at a guess I'd say 10 tons would be high for the probe? So 100 tons for the whole rocket? Just back-of-envelope not-really-thinking it.

[GarrisonChisholm]

Orbit of Kerbin or landing on Kerbin? Also, I assume you want to flyby Eve or Duna, and not land?

I'd go with quite small. Probe core, science, heat shield (semi-optional), and enough fuel for say 2000-2500m/s. Burn at the right time to leave Kerbin and fly by the world (which will be like 1100m/s) and then back at your Sun apoapsis (after the flyby) burn whatever you need to return to Kerbin. If you're good, you can burn at Kerbin and aerobrake a bit to achieve orbit.

This probe will be surprisingly small, so the lifter to lift it should be similarly small. I'm not running the game now but at a guess I'd say 10 tons would be high for the probe? So 100 tons for the whole rocket? Just back-of-envelope not-really-thinking it.

Then, by my non-math, trail-and-error approach, my mission is off by a full Order of Magnitude from your estimate. lol

I'm using a Mainsail for Trans-Eve injection, am planning to make a single distant eliptical oribit (dropping 3 probes going by), and then will be using a Skipper to bring the return stage back to Kerbin Orbit and ultimate re-entry. I'll have to play around with a smaller launch profile, but I've put too much engineering into this thing- come hell or high water its launching. Harumph.

[Admac]

I've made pretty capable biome hopping Duna landers for about 10 tons, So you's probably want about a 20 ton transit stage. Doing it with 30-40 tons in LKO would leave you lots of options for a manned lander on Duna. Like 5Horse said, you'll only need about 2500-3000M/S DV, and less if you leave the lander in duna orbit. I get a little less than 20% payload fraction on launch vehicles, so you'd bee looking at close to 400T on the launchpad for a full feature manned surface mission.

Just orbital, just a probecore I'd say 2-3 Tons is plenty for a solar powered ion probe, meaning your launchpad weight might be as low as 10-15 tons, and that would give you a pretty lavish 4000+ M/S of DV for polar orbits and w/e else.

To do a survey I know I've sent probes under a ton that made it to Duna, and converting to a polar orbit is about the same DV as flying back to Kerbin, so I imagine if you main goal was absolute min weight, you could get under a ton(In LKO).

Edit: Confirmed an Ion probe with a science Jr and Mystery goo with antenna can be under a ton (0.975T) and have 6400 M/S of DV, overpowered reaction wheels, 800 ec and retractable (For aero breaking) solar panels. So lots of fat to cut still, if we were trying to find the absolute minimum.

Edited July 31, 2015 by Admac

[Pecan]

I have just designed an Eve/Duna orbit and return (7km/s to allow for errors) science probe. Science-mode limited so the parts aren't the best possible.

Recovery-stage probe itself is about 1t, while the whole transfer-orbit-return-orbit vehicle is 15t and total launch mass 95t.

Although designed to return that dv does mean it can do anywhere 1-way.

[Superfluous J]

I'm using a Mainsail for Trans-Eve injection ... and then will be using a Skipper to bring the return stage back to Kerbin

Yikes. Thems some powerful engines there. In space, you shouldn't be using those for... well for anything. But that "not anything" should weigh at least triple digit tons. Once it's in orbit of Kerbin.

[Hagen von Tronje]

Orbit-to-orbit can be really small for a probe. Nukes and ions will both give you beautifully compact results though with long burns even on small probes.

If you don't have nukes and ions unlocked and are in middle tech tiers, then a basic build of Mainsail lifter + Skipper midstage/ejector + Poodle final stage should get you pretty reasonable results even if it's on the big side. Though if you do all that, why not send a small pod with it and get the crew/EVA reports, reset the science bay, double collect, and come home with a real haul? It wouldn't be much more massive, and maybe less massive than sending more than one science bay. This lets you get science on moon gravity assists too as a great bonus.

[cantab]

You can easily build lighter, yeah. For the probe itself I typically use an LV-909 with a 200 or 400 tank, that gives me plenty of delta-V to get just about anywhere, and on a light probe the 909 is punchy so there's no waiting around for long burns. This can easily be launched on a launcher that's a swivel-engined core and some SRBs or any other light launcher you have.

But overengineering is fun itself.

[Hcube]

Then, by my non-math, trail-and-error approach, my mission is off by a full Order of Magnitude from your estimate. lol

I'm using a Mainsail for Trans-Eve injection, and then will be using a Skipper to bring the return stage back to Kerbin Orbit

No need to look further... here is your problem. For a flyby mission this is way too big... Just use the smallest probe possible and then go with a few oscar-Bs and an ant engine for around 3000ms of delta V. And this will be super light... then the lifter can be a 1.25m rocket, very small and very cheap. The whole thing should be super light. Just don't use the mainsail for this kind of stuff ! the skipper can be good for super-heavy ships but mainsail is inefficient, heavy and overkill for the job

[Thorbard]

No need to look further... here is your problem. For a flyby mission this is way too big... Just use the smallest probe possible and then go with a few oscar-Bs and an ant engine for around 3000ms of delta V. And this will be super light... then the lifter can be a 1.25m rocket, very small and very cheap. The whole thing should be super light. Just don't use the mainsail for this kind of stuff ! the skipper can be good for super-heavy ships but mainsail is inefficient, heavy and overkill for the job

It is interesting how quickly a small amount of over-engineering can turn into a large amount of over-engineering.

My current (early career) probes are all RCS powered, still manage a significant amount of DV.

[GarrisonChisholm]

Yikes. Thems some powerful engines there. In space, you shouldn't be using those for... well for anything. But that "not anything" should weigh at least triple digit tons. Once it's in orbit of Kerbin.

Agreed; yes, I understand the ISP of the Mainsail is non-ideal for a vacuum task, but the engine is a legacy from when the 2nd stage was required to achieve orbit & a Skipper was found inadequate to lift out of the atmosphere. I don't think the engineering guys down at the plant would be willing to break all those struts at this point to replace it (i.e. too much blood-sweat & tears). I think only a failure to make Eve orbit on the second stage would spur an engine re-design for this first attempt.

@Hagen von Tronje; "If you don't have nukes and ions unlocked and are in middle tech tiers, then a basic build of Mainsail lifter + Skipper midstage/ejector + Poodle final stage should get you pretty reasonable results even if it's on the big side. Though if you do all that, why not send a small pod with it and get the crew/EVA reports, reset the science bay, double collect, and come home with a real haul?" --- You do describe the stage I am at mid-tier, but I haven't yet sent a Kerbal out of KOI, so I want to master the process before sending crew (this is my first game). I will sacrifice the extra science since I know I will be learning a lot on this mission.

However, I clearly see now that for Orbit-and-Return missions in the future I should be aiming for 100 tons on the pad, not 1000. :\ Hey, I'm learning; slowly...

[Padishar]

It is interesting how quickly a small amount of over-engineering can turn into a large amount of over-engineering.

That's exactly what is meant by "the tyranny of the rocket equation"...

[Sobriquet]

Then, by my non-math, trail-and-error approach, my mission is off by a full Order of Magnitude from your estimate. lol

I'm using a Mainsail for Trans-Eve injection, am planning to make a single distant eliptical oribit (dropping 3 probes going by), and then will be using a Skipper to bring the return stage back to Kerbin Orbit and ultimate re-entry. I'll have to play around with a smaller launch profile, but I've put too much engineering into this thing- come hell or high water its launching. Harumph.

FWIW, Here are a couple of links I refer to when crafting a mission. "Rocket creep" is a thing.

Optimal Engine charts

WAC's Delta-V Map

Phase angles

<slowly opens a can of worms> KER is an excellent addition. Immediate reference to core-rocket design information. <backs away slowly>

[Hcube]

1000 tons ! ?? urgh ! for a fly-by, aim for less than 60 tons on the pad !

[Pecan]

...However, I clearly see now that for Orbit-and-Return missions in the future I should be aiming for 100 tons on the pad, not 1000. :\ Hey, I'm learning; slowly...

If it works, it works :-)

If you like aiming for efficient then, yep, you have a new target to aim for. If you like launching big, you've got good experience to start with.

Win either way.

[xtoro]

I made a microprobe that runs on RCS and weighs 0.855t and has 1940dV. You could remove some parts or add more RCS to add more dV. Since it's so small it only needs a tiny rocket to get it in orbit. You can even use what's left in your last ascent stage to start your interplanetary transfer.

Link with download and pics http://forum.kerbalspaceprogram.com/threads/125012-Bitsat-mirco-probe-Cheap-science-at-under-0-9t%21

[SkyRender]

Skipper and Mainsail? Way overkill for your project. Consider something more like this:

It's compact and fully featured, and comes in at under 50T. Comes with: full-science main probe, full-science "dumb probe", enough dV to get to Eve and circularize without aerobraking, enough fuel to return to Kerbin and safely aerobrake with the payload fully intact upon landing. Warning: Light probes are not for everyone. Not for consumption by minors, please consult your doctor before using.

[GarrisonChisholm]

Skipper and Mainsail? Way overkill for your project. Consider something more like this:

http://www.skyrender.net/lp2/ksp/eve_light_probe.jpg

It's compact and fully featured, and comes in at under 50T. Comes with: full-science main probe, full-science "dumb probe", enough dV to get to Eve and circularize without aerobraking, enough fuel to return to Kerbin and safely aerobrake with the payload fully intact upon landing. Warning: Light probes are not for everyone. Not for consumption by minors, please consult your doctor before using.

Wow, that is all with starter engines too?? I'm impressed! This is what I needed to see, to see the "physical" relationships between components, size, & DeltaV. ..and we're sneaking these photos over to the lab right now... *whistles innocently*

- - - Updated - - -

<slowly opens a can of worms> KER is an excellent addition. Immediate reference to core-rocket design information. <backs away slowly>

Yes, I look at the engineering read-outs from other folk's screen-shots with envy. However, for my first play-through I am going completely stock on my at-purchase version number (1.02), and in fact will likely not begin a modded install until 1.1 has been out and proven stable for some time. At the moment, I am enjoying every little engineering project, and feel no lack of joy. :]

- - - Updated - - -

Wow, that is all with starter engines too?? I'm impressed! This is what I needed to see, to see the "physical" relationships between components, size, & DeltaV. ..and we're sneaking these photos over to the lab right now... *whistles innocently*

- - - Updated - - -

Yes, I look at the engineering read-outs from other folk's screen-shots with envy. However, for my first play-through I am going completely stock on my at-purchase version number (1.02), and in fact will likely not begin a modded install until 1.1 has been out and proven stable for some time. At the moment, I am enjoying every little engineering project, and feel no lack of joy. :]

P.S. Oh, the Eve probe is on its way, though with frustrating inefficiency; departure stage had to be used to circularize orbit, & departure burn of 1000 m/sec will require a course-correction burn of another 1000 m/sec to actually get an encounter (bad window read). Highly unlikely the main probe will have the Delta V to return to Kerbin Orbit.

[BlueCanary]

Built around cubic octagonal struts, small probe cores and if you are willing to only use radial attached science parts you can get a simple probe down to around 0.3 tonnes excluding propulsion. It wouldn't be able to do much, but maybe if you pack several on a mission to disperse over an area or something it could be fun. For propulsion on something that size you only need something like an Oscar-B tank and an ant engine to get enough delta-v to go to duna or eve, keeping the total spacecraft weight well under a tonne. So if you're good at launchers and flying efficiently (and I'm not, so I may be horribly wrong about this) you should be able to get a funtioncal, if limited, probe to Eve or Duna at less than 5 tonnes on the pad, and if the science parts are kept to the bare minimum only a few thousand funds.

[SkyRender]

Wow, that is all with starter engines too?? I'm impressed! This is what I needed to see, to see the "physical" relationships between components, size, & DeltaV. ..and we're sneaking these photos over to the lab right now... *whistles innocently*

Help yourself! I can even provide the .craft if you'd like. Also, if you're curious, the tool I use to check dV and TWR is called Kerbal Engineer Redux. It's a very low-impact plugin overall that simply provides extra data (both when building and optionally when flying as well). It's pretty much the spacecraft engineer's best friend.