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I am researching satellite technology, and in particular I am looking at the rise and implications of smallsat technology. As far as I know, there are currently no satellites beyond LEO that would be categorized as smallsats. Here's a link to a list of all or most satellites currently in orbit.

Wikipedia defines smallsats as anything under 500 kg while NASA puts the cutoff at 180 kg.

For Earth-based orbits, it appears that the farther away the satellite, the larger it is. I am just wondering if this will always be the case.

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  • $\begingroup$ There have certainly been many small satellites in Earth orbit farther than LEO. Some into deep space beyond Earth orbit completely. Wikipedia says that small satellites, or smallsats are anything less than 500 kg! But I think you are really interested in the more modern standardized format called cubesats. If you want to ask about cubesats beyond LEO, you should probably edit your question. $\endgroup$ – uhoh Apr 6 '17 at 14:12
  • $\begingroup$ Thanks for your comment. Can you give me an example of a small satellite that has gone beyond LEO? I can't find a single example. I just went through the list in the link above, and I don't see an example in the first 1,000 satellites listed. The lightest GEO satellite I could find was about 700 kg, which is the approximate size of all the MEO satellites. $\endgroup$ – Unistuttgartaerospace Apr 6 '17 at 14:28
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    $\begingroup$ OK please note that you should start using the "@" symbol in front of someone's name if you want to send a message to a certain person. In this case I got a flag in my inbox, but it doesn't always happen. I recommend you define what "smallsat" means within your question, and add a link. Do you want Wikipedias 500kg, or NASA's 180kg (where did you find that, show the link!) or do you want cubesats specifically? $\endgroup$ – uhoh Apr 6 '17 at 14:58
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    $\begingroup$ @uhoh Here is the NASA link. $\endgroup$ – Unistuttgartaerospace Apr 6 '17 at 15:02
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    $\begingroup$ +1 for your edit(s)! The title of your question is "Is it possible..." and of course it is possible. Do you want to know if it is possible, or if it will happen, or do you want to make sure it hasn't happened in the past? Or do you want the answer to completely ignore what has happened in the past? OK good luck! $\endgroup$ – uhoh Apr 6 '17 at 15:20
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Addendum: Apollo 15 deployed the Particles and Fields Satellite into lunar orbit. It returned data from August 1971 to January 1973.

It weighed 36.3 kilograms.

enter image description here

Source

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  • $\begingroup$ Love the photo! Who is the space arti... Ahem. Weren't at least some of the early lunar probes in that mass range as well (at least dry weight), considering they were made partly out of wood? $\endgroup$ – uhoh Apr 7 '17 at 16:37
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This answer mainly addresses the last part of the question "For Earth-based orbits, it appears that the farther away the satellite, the larger it is. I am just wondering if this will always be the case." (NB at the time of answering the question title was "Is it possible for small satellites to orbit in MEO or GEO" which has the simple answer of yes.)

The simple answer is it is likely but not inevitable that satellites launched to MEO and GEO may be larger.

Options

The starting premise is that higher orbits require more energy to get to from the Earth's surface. Thereafter, talking in typical terms:

  1. For delivery direct by the launch vehicle, this will cost more per kg than for a LEO delivery, or the small satellite will have to find a "ride-share opportunity". Small satellites are often small because they are budget-constrained, or at least this has often been true in the past, so the ride-share approach has been the only real option for small satellites. There is no reason in principle why a 1kg cubesat could not have a direct rideshare delivery to MEO, GTO or GEO.

  2. For delivery to an intermediate point the small satellite will need its own propulsion system. For a small satellite to have some potentially significant fraction of the mass is taken by propellant, propulsion hardware, or solar arrays means that the satellite will have less room for the primary payload.

Presently, plausible targets direct deliveries as rideshares are most likely to be GTO because of the large number of commercial missions there. MEO seems plausible with the traffic to deliver navigation satellites and there are even a small number of direct deliveries to GEO, usually on US and Russian government missions.

Rideshare examples

Examples of missions based on direct or near-direct rideshares:

The STRV 1a and 1b satellites (~50kg each) were deliberately launched on a rideshare into GTO as the target orbit so that they could measure the radiation environment and test experimental equipments. See here for further details.

The Spirale satellite (120 kg) was also launched into GTO on a rideshare but manoeuvered slightly to increase the perigee from 200km to 600km to prolong the mission life. The mission was an Early Warning demonstrator and its not entirely clear why it was based in near GTO, it seems quite possible that it was intended to be the forerunner of a GEO mission and used the apogee passes to obtain a GEO like view of the Earth. See here for further details.

Example: launch to GTO then manoeuvre to GEO

As a rough guide, a mission launched to GTO but targeted to manoeuvre to GEO under the power of the satellite could expect:

  • half of its mass to be taken up by propellant if it used a high performance, e.g. 500N, chemical thruster. Such a thruster would probably have a mass of 5kg itself, a 50 - 100 litre propellant tank would be the same again.
  • if a smaller chemical thruster were used, say 10N, its propellant efficiency and its manoeuvre efficiency would be worse still (scaling down of thrusters and longer thrust arcs respectively)
  • if an electric propulsion system were to be used then the propellant mass could be very much reduced but instead a large solar array would be required - 2KW and upwards for the current commercial arcjets and plasma thrusters. Some scaling down is possible at the cost of longer transfer time.

It is entirely possible to do some rough calculations for the manouevres and equipment mass for such a mission or for other orbits though you can see there is a lot to consider; expect there to be a bit of a learning curve.

Short of actually stepping through such calculations its hard to see how this could add up looking like a large payload mass fraction for even a 50 - 100kg satellite, let alone a nanosat / cubesat.

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  • $\begingroup$ Sorry about my "too-ing and fro-ing", and thank you for your answer! Maybe the question really should have been: what sort of operations can smallsats perform in MEO/GEO. The STRV 1a and 1b mission gets at one of the things I had in the back of my mind, namely about lifespan/space debris. The link you sent says that both were "shut off" after 4 years. Were they not sent to the graveyard orbit? And how do we dispose of a 1kg nano-/cubesat in MEO or beyond? $\endgroup$ – Unistuttgartaerospace Apr 7 '17 at 9:25
  • $\begingroup$ @Unistuttgartaerospace No need to be sorry, the to-ing and fro-ing is a normal part of refining a question, its just in this case I wondered if it might continue a while. The "what sort of operations..." is quite an open ended question for this forum or anyone's imagination, not least because of the wide variety of interpretations for "smallsat". $\endgroup$ – Puffin Apr 7 '17 at 9:34
  • $\begingroup$ For "graveyard" the IADC guidelines vary according to the orbit. My first thought without checking is that for GTO the mitigation should be a) change to an orbit with an orbital lifetime below 25 years and then b) passivate the satellite. This is actually the pattern adopted by SPIRALE, they did a small manoeuvre to lower the perigee. For STRV 1a/b (launched long before the guidelines) I'm not sure a) if they even needed to do such a manoeuvre and b) if they had a sufficient delta V capability or c) had any propulsion at all. $\endgroup$ – Puffin Apr 7 '17 at 9:37
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    $\begingroup$ My comment includes spacecraft farther than any Earth orbit as part of farther than GEO. If we plotted median mass as a function of distance, we might indeed see a local peak at GEO - the big multi--kilowatt communications monsters, but starting from GEO all the way to the Kuiper belt, I think there will will be a monotonic decrease. Farther is some mixture of $\Delta v$ and $time$ since launch. I understand you're anticipating the question's Monte-Carloing. :) $\endgroup$ – uhoh Apr 7 '17 at 16:27

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