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Rocket to launch 8 cubesat to LEO at an equidistant distance reminded me that I'd never asked this question. NASA's TROPICS 3U cubesat constellation hasn't been launched yet, so there's still time to ask.

Gunter's Space Page TROPICS says:

The TROPICS constellation will be formulated with four CubeSats in each of three orbital planes with the following launch parameters: equally spaced RAAN (±30° tolerance), 600 km altitude (550±50 km tolerance), 30° inclination (±3° tolerance). These mission parameters will meet science requirements should the threshold number of CubeSats (eight) be implemented. Analyses have shown orbit lifetime of 9 years, well over the expected mission lifetime of one year and well in advance of the 25-year de-orbit requirement. This configuration yields 30-minute median revisit rates with average spatial resolution better than precipitation and all-weather temperature and humidity (PATH) requirements, all from a low-cost, low-risk CubeSat constellation platform.

and includes the image below.

Question: How will these 3U cube sats be inserted into three different orbital planes and phased within each one? For propulsion Gunter says "None"!

note: I'm looking for answers supported by existing information on this mission, not just hypotheses, thanks!

Nation:                USA
Type / Application:    Earth observation, technology
Operator:              Massachusetts Institute of Technology - Space Systems Laboratory (MIT SSL)
Contractors:           Blue Canyon Technologies, Massachusetts Institute of Technology - Space Systems Laboratory (MIT SSL)
Equipment:
Configuration:         CubeSat (3U)
Propulsion:            None
Power:                 Deployable solar array, batteries
Lifetime:              1 year (planned)
Mass:                  4 kg
Orbit:                 600 km × 600 km, 30°

Further reading: Wikipedia and eoPortal

TROPICS: Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats Source

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  • $\begingroup$ I expect the planes would be achieved by different launches, the phasing by the dispensing spacecraft $\endgroup$ – JCRM Mar 9 at 8:24
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There’s a 2017 federal “Sources Sought” for launch services for TROPICS. The relevant part is:

Therefore, 6 to 8 TROPICS CubeSats will be placed in a constellation formation as described in the three scenarios included in the attached document. All of the CubeSats are identical and must be placed into their operational orbit within 60-days (first insertion to final insertion). The launches are anticipated to occur in the calendar year 2020. Information is requested from all interested parties regarding various approaches in order to determine the appropriate balance of cost, schedule and technical risk along with the appropriate level of competition and small business set-aside opportunities. The launch service shall be capable of delivering the mission via single or multiple launches.

So they made it the vendors problem.

They did give a bit of relief in the detailed request document (PDF linked from here) by providing for two-plane and even single plane options as alternatives.

The science team were optimistic that multiple vendors would be interested. A 2017 talk by the PI said the “small satellite launch segment is rapidly maturing” and mentioned Rocket Labs, Virgin Orbit and Vector Space. A 2019 talk said the mission had slipped to 2021, and there’s nothing on the usual Federal contracting sites to indicate that the launch has been awarded (it’s possible that it was part of some bundled contract, however; those can be hard to find)

The team’s intent appears to be multiple launches, because the smaller vehicles referenced by the team can do it no other way. But the NASA contracting process is saying that the solution is up to the vendor.

Until the contract is awarded, the solution won’t be known.

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    $\begingroup$ Thanks! Added a bit at the end to try to make current status clearer $\endgroup$ – Bob Jacobsen Mar 15 at 15:48
  • $\begingroup$ Great, thanks! +1 $\endgroup$ – Organic Marble Mar 15 at 15:50
  • $\begingroup$ I finally found the constellation I was trying to remember for another question, it is CYGNSS and it uses differential drag to attain and maintain phasing within a plane. Both TROPICS and CYGNSS are discussed here. I wonder if a search for "TROPICS" +"differential drag" might turn up something further? $\endgroup$ – uhoh Mar 15 at 23:42
  • $\begingroup$ I'll leave this unaccepted until we find out the answer. Thanks! $\endgroup$ – uhoh Mar 20 at 4:14

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