Submitted via IRC for takyon
A Silicon Valley startup developing electric propulsion systems for satellites has raised $10 million and added the billionaire founder of LinkedIn to its board.
Apollo Fusion announced the $10 million Series B round July 11, bringing the total the company has raised to date to more than $18 million. The round was led by venture fund Greylock Partners, with one of the fund's partners, Reid Hoffman, joining the board.
Apollo Fusion will use the funding to scale up manufacturing and testing facilities for its electric propulsion system, called the Apollo Constellation Engine (ACE). The company believes that ACE is well-suited to serve the growing demand for smallsats with onboard propulsion.
Source: Electric satellite propulsion company raises $10 million
(Score: 2) by c0lo on Tuesday July 17 2018, @11:53PM (3 children)
Just make the satellite all shiny outside and all black inside and insulate the iodine in a dewar flask. In about half a year (gut feeling) thermal radiative losses will bring the fuel close to zero.
In any case, the above is a pure exercise in tech pedantry, even -100C is more than enough to keep iodine reactivity to a safe to ignore level.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by Immerman on Wednesday July 18 2018, @03:28PM (2 children)
From what I can find, the average temperature of a satellite in orbit is approximately the same as it is on the ground, but with greater temperature swings (-170C to 123C from the first google link). Shininess could help, but you've got great big unavoidable heat collectors in the form of the solar panels powering everything, and heat will flow from them down the power cables if nothing else.
(Score: 2) by c0lo on Wednesday July 18 2018, @03:47PM (1 child)
As long as the radiative loss of heat from the fuel tanks is greater than the rate of heating due to direct contact, the fuel tank is going to cool down.
It may not reach into fraction of Kelvin but for sure proper arrangements can be made to have it dropped below -100C.
(e.g. no need for the power cables to reach the tank - heat the fuel when needed by electron beams. No need for the tank to be fixed using large contact brackets once in space, as an ion engine is not exposed to high accel, simple point-contact "brackets" suffice; support the tank during escape from Earth grav, then eject the massive support and keep something with minimal surface contact to the fuel tank itself).
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by Immerman on Wednesday July 18 2018, @07:42PM
Yeah, that might work, though there's a certain amount of unavoidable thermal contact in the form of the fuel line. And there's lots of active cooling techniques you could employ as well. If orbital research equipment can be held at cryogenic temperatures, I'm sure a fuel tank can be chilled to something much more moderate.
That radiant heat transfer from the tank does fall off quickly though. Radiant emissions are proportional to the 4th power of the absolute temperature - so cooling from a mild 15C (288K) to -100C(173K) means your radiant emissions have fallen to only 13% of their original levels, and the interior of the satellite will be shining back much more strongly, regardless of color. Better have a really shiny fuel tank, and a thermally insulated fuel line. Might need some more active refrigeration system to supplement it