dV maximum theoretical for IP

[kahlzun]

Ok, so I'm building a set of omni-ships, ones that are designed to land or return from everywhere in the Kerbol system.

I'm currently trying to work out the dV required of the interplanetary stage, to ensure it is capable of travelling everywhere.

On that note, I am trying to calculate what dV I would require to intercept Eeloo at its worst possible position of 113,549,713,200 m, more-or-less shown here:

(Yes, I know that is not the correct phase angle for Eeloo, i just need the dV)

I have looked at the equations here and got this thing:

v1 = SQRT((r1*(r2*v22-2*μ)+2*r2*μ)/(r1*r2))

where:

r1 = parking orbit radius

r2 = SOI radius

v1 = ejection velocity

v2 = SOI exit velocity (absolute value)

µ = gravitational parameter of origin planet

Unfortunately, it does not go into how to define v2, and so leaves me with bupkis.

So, kerbalnauts I ask: How much extra dV would I need to increase my solar orbit from 13,599,840,256m (Kerbin) to the furthest point of intercept- 113,549,713,200m (Eeloo) (Interesting to note how close they are to exactly 100 billion m difference).

I don't need the inclination burn calculations, but if you feel the need to include them, please seperate it out so it is clear which is which.

Thanks.

[Jesrad]

"Once you are in orbit, you are halfway to anywhere", aptly said Robert Heinlein. In your case v2 is 841 m/s, if that can help. It's the base escape velocity for the destination object.

My own calculator for interplanetary travel gives me these figures:

917 m/s for escaping Kerbin from 100 km orbit

2955 m/s for the Kerbin/Eeloo transit, 3123 m/s if I use the Ap distance of 113,549,713 km (that's the number you're looking for)

224 m/s for parking at a 50 km altitude orbit at Eeloo

Total dV=4265 m/s

Edited May 17, 2013 by Jesrad

[Itsdavyjones]

I'd say 5k delta v for plane changes and a safety margin.

[Temstar]

If the aim is to be able to get to any planet then Eeloo is not the worst case, Moho is worst case by a long shot and transfer costing 7km/s to Moho orbit is not uncommon.

[numerobis]

The speed you want when you leave the SOI is the first burn in a Hohmann or bi-elliptic transfer.

You do the symmetric calculation in order to calculate the orbit insertion burn at Eeloo, since it has no atmosphere.

If you want to land and return, the worst case by far is Eve. You might want to ignore that case though, and just be mostly universal.

Edited May 17, 2013 by numerobis

[kahlzun]

If the aim is to be able to get to any planet then Eeloo is not the worst case, Moho is worst case by a long shot and transfer costing 7km/s to Moho orbit is not uncommon.

according to the calculator thingy, the Ejection Velocity for Moho is "3942.16 m/s" and Eeloo is "4315.23 m/s".

The inclination of Moho isn't that bad, is it?

[Temstar]

according to the calculator thingy, the Ejection Velocity for Moho is "3942.16 m/s" and Eeloo is "4315.23 m/s".

The inclination of Moho isn't that bad, is it?

Yeah it's that bad. It's not just the inclination either, the relatively elliptical orbit of Moho tends to mess up interplanetary transfer big time as none of the phase angle calculators take eccentricity into consideration. Therefore your average Moho transfer looks like this:

About 1680m/s at the start of the transfer to reach Moho orbit

1380m/s inclination and phase adjustment burn to set up correct Moho encounter. You can see I managed a pretty good phase angle here, didn't need to dip inside Moho orbit. If you need to dip inside due to eccentricity throwing off the phase angle then that mid course adjustment is going to be even worse.

On arrival, a 4000m/s+ burn to insert into Moho orbit.

[Specialist290]

Temstar's screenshot looks a lot like my own most recent experience. Usually takes me about ~1900-2000 dv on the initial burn (usually because I try to plot for an intercept straight from the bat), maybe 300-500 dv of midcourse corrections, and then anywhere from 4000-4500 dv to capture.

Most delta-v maps don't reflect this, as I think they assume a circular orbit in the same orbital plane.

[kahlzun]

So, hoiw much dV would my IP stage need to have to 'safely' reach all planets? (it's a one-way probe lander)

[stupid_chris]

If you want to leave yourself error margins, and have spare fuel to adjust your orbit (eccentricity, inclination, etc.) around any body or the Kerbol system, I would say 7000m/s should be good. That isn't calculating any potential landing. For example, I have a mapping probe, and I'm sending one to each body to with the ISA mapsat mod and the kethan mod for potential exploitation, and it's rigged up to A lot of fuel and a NERVA engine and it has 7300m/s of fuel. My two worst case for sending it were Eve and Moho. Eve because I made a burn error and found myself on a 5000km periapsis instead of 300 as I expected. Result: after doing my capture burn, lowering my orbit, then switching to a polar inclination, I only had 500m/s left. And Moho is really fuel demanding, I had a 3500m/s 8min burn for capture. Thats already half my delta v. So if you want to have the worst case scenario and error margin, I'd say 7000 once is LKO is your best shot.

[stupid_chris]

then if you want to land a small probe, it depends on the body, you can go from like 200m/s on Gilly to a lot (idk how much exactly) on Tylo, the biggest non atmospheric body. Else, parachutes will do the job.

[kahlzun]

Oddly enough, landing is easy. Using the 24-77 engines, a T200 tank is enough to land a bare-bones probe on Tylo from a 100km orbit with a bit to spare:

Hyperedit, go

(this is the lander I'm building the IP stage for)

There isn't much wiggle room, but it has a chute and everything you need to land ANYWHERE.

[stupid_chris]

it is easy, but it just recquire a lot of delta V since it's gravitational force is quite large. And for something that small, I think putting a T800 tank underneath this with a Nerva engine and a pair of jettison-able T800 tanks on the side should get you enough delta V. I'll check this out as soon as I can and I'll post pictures

[stupid_chris]

Alright, test results:

Alright so the design I came with is quite simple and light. It has solar panels to be sure to keep power during the interplanetary drift, a bit of rcs for control and the two T400 tanks on the side or jettisoned once they have been emptied (I know, space junk, but it gives an extra 500m/s). It has 7107m/s of delta V, which should make it capable of going to any planet or moon in the kerbol system. I tested it on Moho, the most delta V requiring plantet.

Edited in circular 100kmx100km orbit around kerbin.

1800m/s 7min burn for Moho transfer.

1200m/s 4min burn to ajust closest approach to 100km

Jettisoning the tanks during the burn. Sorry for the thrash.

Moho periapsis at 1200km. Hmm, not what I asked for. RCS adjustment lowers it to 100km in a few taps though.

3500m/s 8min burn for Moho capture. It's quite expansive indeed.

After circularisation, my remaining delta V was of 500m/s and my orbit was polar, which is not enough to switch it to an equatorial orbit (with the lander it could have been achieved but I didn't want to do this for nothing as we're just landing).

Instead, I used what was left to lower my periapsis, then begin my deorbiting burn, setting the empty tank and engine on a collision course with Moho after decoupling.

Landing was a breeze, plenty of fuel left, so I just decoupled the skycrane and sent it crashing on the planet too as it wouldn't be of use (yes I know I set the decoupler on the wrong direction on the probe ). This is also why I moved the MechJeb case to the crane, it allows control after decoupling to send it elsewhere.

So yeah, you can retake this design if you want to or just inspire yourself from it, building a launcher for it would be pretty easy as its only 14t. Hope I helped

If you need help with anything else don't mind asking ^^

Edited May 18, 2013 by stupid_chris

[kahlzun]

That design was more-or-less my plan, I just needed a datapoint on the required IP dV. Turns out i've been over-engineering my IP stages for ages, I usually try to get about 9000 dV, so it's good that I can reduce that a little. Thanks.

[stupid_chris]

No problem ^^

[kahlzun]

If you need help with anything else don't mind asking ^^

Ok, been working on a design, and I have a new question: If I was to build a 'mothership' style IP stage, which went to -wherever-, and then flew back to Kerbin, how much dV would we need?

From the earlier answers, dropping your orbit requires the most dV, so the return from Moho should be relatively light: would the deceleration from Eeloo be the killer in that instance? I guess Kerbins atmo provides a nice easy braking mechanism, but how much dV would i need to do it safely?

[John FX]

If the aim is to be able to get to any planet then Eeloo is not the worst case, Moho is worst case by a long shot and transfer costing 7km/s to Moho orbit is not uncommon.

I agree Moho is the worst place for Dv cost. Tylo is a bad case as well because you have to burn to jool (sometimes further than Eeloo) , get into jool orbit then burn for tylo SOI, burn for tylo orbit and then tylo itself is almost the size of kerbin with no atmosphere. That`s 5 chances to cost yourself extra Dv...

[John FX]

Here is a stock lander for a single Kerbin that will go anywhere in the system and land.

https://dl.dropboxusercontent.com/u/12775588/GM%20Universal%20Lander%202.craft

[kahlzun]

Here is a stock lander for a single Kerbin that will go anywhere in the system and land.

Thankyou for that, I was more asking about a land-and-return craft than a one-way 'coloniser' craft.