Radio telescopes are way bigger and heavier (large dishes required). Even more importantly, usually many radio telescopes are used together for interferometric observations. They require exquisite calibration of the distance between the telescopes, which can be pretty difficult in space.

Actually not necessarily. Many light, cheap and small antennas can also work.

See p.8 and 10 for those used in the current state of the art telescope at 160MHz https://www.aanda.org/articles/aa/pdf/2013/08/aa20873-12.pdf And https://cdr.skatelescope.org/#photos?lfaa for those used in the SKA, one of the largest future radio telescopes that is still under construction.

Getting the distances between the telescopes is actually easier in space. Both distance measuring and datatransmission could be done with lasers when there is a clear line of sight. Moreover, once an orbit is established, the laws of Kepler are 'followed' and predicting their mutual distances is something we can do extremely well. On Earth with very long baselines it is much trickier and things that need to be taken into consideration are cablelength differences due to temperature changes, tides and continental drift. (Continental drift is actually measured with radio telescopes: in the reverse problem when the location of a set of sources on the sky is known to high precision one can establish at what speed the distances between the telescopes is changing.)

You might want to look into what the NRO is already putting in space (supposedly) [1]. If the reports are to be believed, 100m dishes are already there, just pointing at the earth instead of into deep space. To your second point, it seems that relative positioning is mostly a solved problem at least for satellites in GSO (that's a core part of how GPS works). My personal opinion is that space-based radio astronomy is mostly a problem of cost, not of available tech.

[1] https://en.wikipedia.org/wiki/Orion_(satellite)

Not a solved problem, GPS is too inaccurate for interferometry. The problem is you want to do correlations between radio signals; consider a 1 GHz signal, which has a 30 centimeter wavelength. Error compounds as you integrate longer and longer signals. To do anything decent, you need to know absolute position within millimeters, and it can't be drifting too much.

Also, the positioning error isn't the whole story; there's also timing drift. Rubidium GPS-disciplined oscillators actually drift too much instantaneously to be useful...

Laser interferometry will pinpoint the distance to far less than a millimeter.

Military spacecraft are almost always ahead of scientific ones, and a 100m foldable dish might be an engineering marvel, but it's a bit different from a 100m telescope. An actual telescope needs to guarantee that your data are correct within certain tolerance, and not just good enough to get a good SNR from another spacecraft.

Besides, as another poster noted, VLBAs need extremely precise positioning which is just another rabbit hole. Spektr-R orbit determination was really tricky for its baseline of 300000+ km.

I've always thought on the moon would be more interesting than "beyond" the moon. A ground-based dish on the dark side of the moon, isolated from a large majority of the noise we're pumping into space by the body of the moon itself.

But it wouldn't collect the type of data that will be lost by the 5G spectrum. We can't change the microwave emission frequency of water but we can change our technology to not use a frequency close enough to cause interference with that frequency.

Large dishes and large networks of large dishes are economical on the ground in ways that are utterly impractical in space.

Yes and no. Those large dishes on earth require massive support structures. In the zero gravity of space large dishes can float virtually unsupported. There are spy sats with extremely large reflectors. The biggest geostationary ones can been seen from earth, meaning they have reflectors on the order of 100m+ in diameter. Turn one of these around and we would have a very capable radio telescope, much as how a redesign of another spysat program gave us hubble.

https://en.wikipedia.org/wiki/USA-202

https://en.wikipedia.org/wiki/Orion_(satellite)

For the low, low price of 2 gigabucks each.

For an idea of scale, the entire VLA was built for ~80 megabucks. The entire Atacama Large Millimeter Array was built for 1.4 gigabucks.

Gigabucks and megabucks is how I’ll be talking of money from now on.

Totally worth it, even if to just add momentum to building space infrastructure and increase world's competence in space technologies.

Things have changed quite a bit over past 20 years. Launches are getting much cheaper now, and satellites are getting smaller. I imagine costs could be brought down, especially if the scope of the mission was limited to e.g. simple constellation for radiointerferometry.

More like shouldn't the government have prevented 5G from licensing the spectrum in the first place?

We have already done a few low-Earth-orbit radio dishes for VLBI [0]. IIRC correlating the data from a single on-orbit dish was difficult because it was moving way faster, over larger distance, than the other elements of the array. Still learning how.

[0]: https://tinyurl.com/google-search-vsop

More info on impact of satellite constellations on radio astronomy: https://news.ycombinator.com/item?id=19712625

In addition to the good points raised nearby: The data rate from radio telescopes is enormous.

Just put a 5G tower on the radio tele... nevermind.

Data rates are high for the particular types of astronomy being done today because they are the cheaper capability. Adding new electronics to existing telescopes is less expensive than building a larger dish. But any astronomer would trade those date rates for the greater sensitivity/resolution and decreased noise of a massive space-based dish.

The stream is also in one direction.

I suspect an optical (laser) emitter could transmit either directly to Earth or to a retransmission satellite at GSO that already has a beefy radio downlink, and also serves as a regular comm sat.