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MCCreeper8890

How much DeltaV to get to 150km equatorial orbit?

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Hi. I'm trying to make (the start of) a space station in this wonderful game. I have a 7.2 ton payload that I would like to get into a specific orbit. In short, how much DeltaV is required to get up to a 150km equatorial, fairly circular orbit? And, is there a "rule of thumb" for this kind of stuff?

Please keep in mind that I am a fairly inexperienced player (kind of weird that someone like me would be trying to make a space station), so add about 500-1000m/s extra DeltaV.

About me being inexperienced, I currently have 2 probes and a refuel vessel in a 300km orbit, as well as a considerable amount of debris stuck in LKO.

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Welcome to the forum :)

Let's take a look at the 'DeltaV Map' :)

 

It can be tricky to read for the first time, so let me give you an example:

'Kerbin' as home planet is right at the bottom. To get up in a 80km circular orbit, an ideal flight would need 3400m/s dV. A circular Keostationary Orbit (2863km) would require additional 1115m/s dV and sums up to a total of 4515m/s dV.
Lets get back to the 80km and pretent, you want to go to the Mun. This will require 860m/s to reach a hyperbolic (fly-by) trajectory, 310m/s to reach a circular orbit at 14km, and 580m/s to land on the surface. The sum of all dV values is 5150m/s. You can find all these values in the map, so I hope it will help you to understand this great tool ;)

All these values are calculated for an ideal flight, so you can add your 500 - 1000m/s to get some fuel to spare. To raise your orbit from 80 to 150km, it does not need much, so may add 100m/s extra just to raise your orbit. In total, I would suggest to try ~4200m/s dV.

32 minutes ago, MCCreeper8890 said:

a considerable amount of debris stuck in LKO.

You can use the tracking station to terminate the debris. I'm not sure about the default settings, so you may have to move your cursor to the top of the screen to bring down a little bar to select which kind of vessels are visible in the tracking station (accounts for the map view as well). The debris symbol looks a bit like a fuel tank.

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Posted (edited)

It's not entirely clear what it is you are asking for.  Get up to 150 km orbit from where?  It should take about 120 m/s or so more to reach 150 km than will to get into a minimum orbit just about Kerbin's atmosphere.

(edit)  The general rule of thumb is that a launch vehicle requires about 3400 m/s to attain a minimum orbit around Kerbin, say 70-80 km altitude.  To launch directly into higher orbits, the extra delta-v that it takes is about the same as that required to perform a Hohmann transfer from a low to the high orbit..

Edited by OhioBob
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Yeah. Launching through an atmosphere costs you quite a bit of extra dV over the theoretical optimum -- especially if your payload is not nicely streamlined (which spacestation parts usually aren't). So I'd suggest that 4500 would be fairly typical -- and then you can judge your degree of piloting awesomeness as to how much extra you have left over beyond that. Fuel tanks with leftover fuel are very nice things to have attached to a spacestation too.

I actually make entire careers devoted to saving my boosters, and building the spent stage1's into big spacestations.

And yeah, debris in LKO is a pain. Other players build careers around keeping LKO clean by deorbiting debris. As Mr. cheesecake said, you can terminate it from the Tracking Station. You can set the game to clean it up automatically (which has some dangers, because one game's debris is another man's treasure). Or you can build a bunch of little spacetugs that fly around and collect debris to do something or other with it.

 

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It's a relatively small payload and not too far above minimum orbit. Providing it has a reasonable TWR on the first stage about 4000m/s vacuum on the launch pad should be more than enough. A simple 2.5m launcher with a twin boar first stage and a poodle+8 tonne tank second stage will do it with good margins.

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On 7/29/2018 at 1:00 PM, 4x4cheesecake said:

You can use the tracking station to terminate the debris. I'm not sure about the default settings, so you may have to move your cursor to the top of the screen to bring down a little bar to select which kind of vessels are visible in the tracking station (accounts for the map view as well). The debris symbol looks a bit like a fuel tank.

I have already done that. An update on my space program: 3 probes in 300km orbit, and a refuel unit. All orbits corrected and within a narrow band (one of them had an unacceptable inclination). My new goals are exploration to the Mun, and a space station in LKO. I only wanted a 150km orbit in the first place to dodge debris left from other missions.

Also, I kind of regret terminating all of that debris. because it formed a nice belt around Kerbin.

So, we can kind of forget about this whole conversation, because it will get to LKO. Also, does it really only take ~600m/s to transfer from LKO to 150km Kerbin orbit?

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5 hours ago, MCCreeper8890 said:

Also, does it really only take ~600m/s to transfer from LKO to 150km Kerbin orbit?

Without any inclination changes, it is actually less then 600m/s. Depending on your initial orbital altitude (probably 70km - 80km), it will only take 100m/s - 120m/s to raise your orbit to 150km.

I've underlined 'raise' because as far as I know, there is no offical definition of LKO. The wiki tells about 70km - 200km to be an LKO, some people refere to this term for an orbital altitude up to 400km (I like to use the term for an orbital altitude up to 300km), so depending on your defintion, you can also transfer from a higher altitude to an 150km orbit. The amount of dV to lower your orbital altitude from 300km down to 150km is pretty much the same, maybe slightly more (up to 200m/s).

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A low Earth orbit is considered to be anything up to about 2,000 kilometers.  I think officially it's considered anything that makes at least 11.25 orbits per day, which works out to an orbital period of 128 minutes or less.

In KSP I usually consider low orbit anything below 250 km, because that's the border between "in space low" and "in space high" for science experiments.

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On 7/31/2018 at 8:29 AM, OhioBob said:

A low Earth orbit is considered to be anything up to about 2,000 kilometers.  I think officially it's considered anything that makes at least 11.25 orbits per day, which works out to an orbital period of 128 minutes or less.

In KSP I usually consider low orbit anything below 250 km, because that's the border between "in space low" and "in space high" for science experiments.

Turns out that LKO is 100-200km, and HKO is anything greater than 230km. At least, that's what I remember...

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Posted (edited)

You would want to put the station into an orbit of at least 120km, by the way. Specifically for rendezvous and stuff.

I tore apart my communications network, thinking I could come up with a better probe, but I really only redesigned my OKTO based probe :P

By the way, this is how Jebediah Kerman is often portrayed: :cool: (probably because he IS cool)

Edited by MCCreeper8890

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1 hour ago, MCCreeper8890 said:

Turns out that LKO is 100-200km, and HKO is anything greater than 230km. At least, that's what I remember...

Is the Wiki wrong?
https://wiki.kerbalspaceprogram.com/wiki/Science

Celestial body multipliers

Each celestial body has different multipliers applied to the collected scientific data, based upon where it is taken in relation to that body. Biomes do not affect these multipliers.

The altitudes given in this table determine the altitude above mean sea level of the boundary between lower and upper atmosphere and between near and outer space. The upper atmosphere extends to the atmospheric height and the outer space extends up to the end of the sphere of influence.

  Surface Atmosphere Space   Total
Celestial body Landed Splashed Low High Border Limit Low High Border Recovery Total Science Total Data
Kerbol N/A N/A 18 km 600 km 11× 1000 Mm    
Moho 10× N/A N/A N/A N/A N/A 80 km    
Eve 22 km 90 km 400 km    
Gilly N/A N/A N/A N/A N/A 6 km    
Kerbin 0.3× 0.4× 0.7× 0.9× 18 km 70 km 1.5× 250 km    
Mun N/A N/A N/A N/A N/A 60 km    
Minmus N/A N/A N/A N/A N/A 2.5× 30 km 2.5×    
Duna N/A 12 km 50 km 140 km    
Ike N/A N/A N/A N/A N/A 50 km    
Dres N/A N/A N/A N/A N/A 25 km    
Jool N/A N/A 12× 120 km 200 km 4 Mm    
Laythe 14× 12× 11× 10× 10 km 50 km 200 km    
Vall 12× N/A N/A N/A N/A N/A 90 km    
Tylo 12× N/A N/A N/A N/A N/A 10× 250 km    
Bop 12× N/A N/A N/A N/A N/A 25 km    
Pol 12× N/A N/A N/A N/A N/A 22 km    
Eeloo 15× N/A N/A N/A N/A N/A 12× 10× 60 km 10×    

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Posted (edited)
5 hours ago, Blaarkies said:

Is the Wiki wrong?

No.  The delineation between In Space Low and In Space High is still at 250 km.  However, Low Kerbin Orbit is not a well-defined term:  in common use, it can cover anything from 70 km up to about 200 km, but there's nothing specifically enforcing that; it's just what people posted in Mission Reports.  Some people describe a Medium Kerbin Orbit, but some don't, and some only define High Kerbin Orbit up to the synchronous orbit, even though technically, orbiting beyond Minmus at 80,000 km can still be called High Orbit.

I've seen one useful system that still isn't 'official'--whatever that means--but nevertheless has well-defined and specific strata:  Very Low Orbit is anything from 70 km to 120 km, Low Orbit is anything from there up to 240 km, Medium Orbit is anything from there to 480 km, High Orbit is anything from that up to 600 km, and Very High Orbit is anything from 600 km and higher.  The astute will note that these altitudes correspond to the availability of higher levels of time warp.

On 7/30/2018 at 8:29 PM, MCCreeper8890 said:

Also, does it really only take ~600m/s to transfer from LKO to 150km Kerbin orbit?

Orbital velocity at Kerbin's surface is actually 2426.1 m/s, aside from the explosions and fire and lithobraking.  Orbital velocity at 70 km is 2295.9 m/s, and orbital velocity at 150 km is 2170.0 m/s.  @4x4cheesecake already gave the correct value for the transfer; my own calculations show the ideal delta-V to be 125.8 m/s to go from a circular 70 km orbit to a circular 150 km orbit, but it would be less if you started higher.

Remember that Kerbin's rotational velocity at the surface is 174.9 m/s:  the reason it takes so much delta-V to reach orbit is not because you need to go from 0 m to 70 km high, but because you need to go from 175 m/s surface speed to approximately 2300 m/s orbital speed, all while ploughing through an atmosphere.  Once you have orbital velocity, though, subsequent changes are relatively cheap.  You already have most of the orbital energy you need; you're not starting from near-zero.  To put things in perspective, if we assumed that Kerbin had no atmosphere, no terrain, and that we wanted to first orbit at the surface, it would cost about 2250 m/s to go from the pad to a theoretical 'surface orbit' and from there it would only be another 130 m/s to get to a 70 km orbit.

Edited by Zhetaan
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To choose a Kerbin station altitude go with what makes sense based on where are likely visiting ships arriving from and where are they going after leaving?  If the majority of stuff is coming up from Kerbin and going back down to Kerbin, you'll want a lower orbit just to lower the dV requirement from the surface.  If stuff is coming in from the moons or planets and going back out it makes sense to go to a higher orbit to save these ships dV slowing into and climbing back out of Kerbin's gravity well.

FWIW, I go with 80km around Kerbin which is also the initial orbit I launch most rockets. I tried a station at 120km once and the extra dV on station missions wasn't worth it to me especially when you start talking 40+ ton payloads to the station. I'd guess 99% of the arrivals at my LKO station come from Kerbin's surface and initially a lot of these are heavy.

 

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