Wednesday, April 26, 2017

Project Destiny: Interplanetary Communications Network

This is a topic post referring to Purdue University's project Destiny.
Here is my introductory post for the series.
The subject is section 4, Interplanetary Communications Network.

 Headline results: I believe that the cost of this system can be reduced by nearly 50% without altering the underlying performance assumptions.

Details after the break.

Purdue University's project Destiny

Purdue University's School of Aeronautics and Astronautics recently released a feasibility study of Elon Musk's Mars colonization plan. I recommend a look at their full report and appendices if you have some time on your hands and an interest in colonization.

This was a student-run project in collaboration with Dr. Buzz Aldrin and Dr. Andy Aldrin, completed in a single semester. Given the time constraints and the scope of the project, the results are remarkable. While the final report could have used a good science editor's advice, look deeper. The underlying approach is sound, and there is a wealth of details on techniques for designing everything from a water tower to an interplanetary communications network.

At around 1,200 pages for the two primary documents, there is a lot of ground to cover. The entire end to end architecture for putting a million people on Mars within 100 years and keeping them alive is explored. I intend to write a series of posts addressing key points of the study in detail. I have not contacted any member of the team, so this is unsolicited and in no way meant to impugn their work. Their results are very impressive.

Friday, January 6, 2017

'Carrier' spacecraft in the news

Here's an IEEE article describing two planned multi-satellite missions.

One is the Sherpa vehicle from Spaceflight Industries, set to fly on a Falcon 9 as a secondary payload on the Formosat 5 mission. This is expected to launch some time this year, so keep an eye out. The vehicle is described as a space tug by SI, and is capable of carrying mixed configurations of smallsats, cubesat launchers and other custom hardware. This first flight offers an 87-satellite capacity. The vehicle itself seems to be very flexible, with options for additional propulsion and add-on services.

 Another is the Indian Space Research Organization's C37 mission on PSLV, expected to launch near the end of this month. This is a medium-lift vehicle reaching polar orbits, with multiple upper stage restarts available. This launch system has already deployed multiple satellites to different orbits in one launch. Their next launch is expected to deploy over 100 cubesats and two rideshare satellites as secondary payloads to the Cartosat-2d mission.

These craft are significantly smaller than my proposal. That's not surprising; even though the smallsat market is rapidly growing, there just isn't enough demand to justify launching a thousand or more of them a year. It will also take time to develop technologies on this scale that can be used beyond LEO; cubesats face unique and difficult challenges when they can't easily be reached by ground-based communication. This is one of the reasons I focused on the carrier craft providing local comms and possibly beamed power. Sherpa in particular has the volume, mass and technical ability to add a comm relay in the future. One problem with that idea is the payloads drift after deployment; for anything more than short-term experiments, a network of LEO commsats providing data relay services would be a big help.

Edit:
The upcoming Iridium NEXT constellation (first launch expected this month) will offer satellite crosslink services. Spacecraft in polar orbit with appropriate receivers would have access to high-quality redundant communication paths, while their operators would receive data from ground stations over the internet or via an Iridium terminal. We might soon be able to say 'There's an app for that' to people wanting to control cubesats from their smartphone.

Exciting times.