I was just curious why this isn't possible because it's clearly been considered based on the existence of them in the ISS for keeping the facility online. I'd appreciate some clarity on this. Thanks a lot.
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9$\begingroup$ Because (today's most) rockets don't burn electricity. $\endgroup$– user3528438Commented May 8, 2020 at 17:57
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$\begingroup$ Electric engines using lithium ion batteries are getting pretty common now though. $\endgroup$– bobthebuilderCommented May 8, 2020 at 18:05
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1$\begingroup$ @bobthebuilder - by "electric" do you mean the turbopumps, like Electron? Or do you mean ion thrusters? $\endgroup$– IronEagleCommented May 8, 2020 at 20:37
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2$\begingroup$ @bobthebuilder how do you move in space with just electricity? $\endgroup$– TimCommented May 9, 2020 at 13:36
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1$\begingroup$ Because humans have not yet invented electric powered reactionless thrusters. To get anywhere in space, you need reaction mass. (Or a solar sail.) That reaction mass needs to be accelerated (see Newton's Laws), which you can do with either the chemical energy of the mass, as in a conventional rocket, or with electricity, as in an ion thruster. $\endgroup$– jamesqfCommented May 9, 2020 at 16:46
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3 Answers
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The ISS does not have any sort of electric propulsion system. It uses ordinary chemical rockets, either on visiting vehicles or its own rockets which are refueled by such vehicles. (https://en.wikipedia.org/wiki/International_Space_Station#Orbit) Its solar panels are for running its experiments and other equipment.
There is only one rocket that uses lithium batteries as an energy source for its propulsion system (the Electron), and it only uses them to drive pumps for its kerosene and liquid oxygen propellants, which provide the energy for actually propelling the vehicle. When it's out of those, there's no point in recharging the batteries, there's nothing left to pump.
There are many spacecraft and satellites that use ion thrusters, and every single one of them uses solar power to run them...batteries alone could never store enough energy to get anything useful out of such thrusters. Also, while they use electrical power, they use it to accelerate propellant from an onboard tank. There is no "pure electric" thruster (excluding photon rockets, which have impractically high power requirements).
answered May 8, 2020 at 23:36
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The majority of rockets (here meaning "launch vehicles") don't have much need for continued large amounts of electric power, and often don't need to operate for more than a few hours. Electricity is only used to power computers/guidance and controls, while bulk mechanical power is provided by compressed gas, gas generators, pyrotechnics, and turbopumps. All the fuel is burned in a short period getting into orbit, and perhaps a bit more after a restart to adjust orbit or eject into a geostationary transfer or interplanetary orbit, and after that the rocket stage is no longer useful.
For all existing or planned launch vehicles, propulsion is provided exclusively by chemical rockets which, with a few blazing exceptions, are not electrically powered (and the ones that are, such as the Electron, only use electricity to pump fuel into the engine).
(This is in contrast to satellites and probes of all kinds, which normally have solar panels or RTGs and have plenty of power needs. Additionally, manned spacecraft typically have fuel cells or solar panels to provide power -- but this power is still not normally used for propulsion.).
As a result, most launch vehicles don't benefit from having solar panels.
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1$\begingroup$ "Electricity is only used to power computers/guidance and controls" sounds pretty important vs "don't have much need for electric power," $\endgroup$ Commented May 9, 2020 at 14:30
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1$\begingroup$ @Organic Marble: Important, yes, but you don't need a lot of electricity to run them, so a battery or two does the job - and you can launch your vehicle at night, too. (And for the answer, note that a lot of manned space missions, like Apollo, used fuel cells instead of, or in addition to, batteries.) $\endgroup$– jamesqfCommented May 9, 2020 at 16:50
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$\begingroup$ It's good practice to launch at night if you are going to land on the sun :) $\endgroup$ Commented May 9, 2020 at 18:36
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$\begingroup$ I mean that a pretty circumscribed (and small) amount is needed, not that it isn't important to have some. $\endgroup$– ikraseCommented May 17, 2020 at 0:33
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Deep space probes are (mostly) launched using two stage rockets. The first stage is not used after burnout and separation, recharging batteries of the first stage does not make sense. After separation of the first stage there is no connection of the space probe to the first stage.
The second stage is used to give the probe the neccessary speed and direction to the target of the probe. After burnout the second stage is not useful for the probe anymore and is separated from the probe. So recharging the second stage does not make sense too.
Solar panels attached to the rocket itself would only reduce the payload weight. So the possible space probe weight would be reduced.
But solar panels may deliver power to the space probe if the distance to the sun is not too far. During the flight through the atmosphere the probe and the solar panels may be damaged by atmospheric drag, therefore both are protected by a cover called fairing. As long as solar panels are under the fairing or not unfolded yet they generate no power.
To be not damaged by the acceleration of the second stage, solar panels of the probe are unfolded not before burnout and stage separation.
