Early next week, a team of volunteers will use the Arecibo Observatory in Puerto Rico to see if they can make contact with a spacecraft that hasn't fired its thrusters since 1987. If all goes well, the effort could bring the 35-year-old spacecraft, the International Sun-Earth Explorer 3 (ISEE-3), back into position near the Earth, where it could once again study the effect of solar weather on Earth's magnetosphere.
It will be a race against time. ISEE-3, which is transmitting two carrier signals, only came into hearing range a couple of months ago. Dennis Wingo, CEO of California-based Skycorp Incorporated, and his colleagues reckon ISEE-3 still has enough fuel to make it back to its original orbit at the Lagrangian point L1, at a spot between the sun and the Earth where a spacecraft can stay in sync with Earth's orbit. But to make it, Wingo says, the spacecraft must be commanded to fire its thrusters by mid-June.
And that's far easier said than done. NASA no longer has the hardware to communicate with the ISEE-3. So in April, Wingo and Keith Cowing, a former NASA employee and editor of the websites NASAWatch and SpaceRef, started a (still-running) crowdfunding campaign on RocketHub to develop what they need to communicate and control the spacecraft: signal modulators and demodulators, transmitters, and a software-based mission control console to monitor the spacecraft’s propulsion and attitude control systems.
Building all of this even 10 years ago "would have been impossible," Wingo says. But with the advance of embedded systems technology, the team can construct radio components in software and debug them on aggressive timescales without breaking the bank.
With no time to wait, the team has already purchased software-defined radio peripherals built by Ettus Research, which can be used to implement modulator and demodulator programs that would once have had to be built in hardware.
Ettus has volunteered to help with the programming, and one member of the company will join Wingo in Arecibo. They'll set to work there on 19 May, using a 400-watt transmitter shipped in from Germany to try to make contact with the spacecraft. One of the first things they'll do is command the spacecraft into engineering telemetry mode, where it's hoped it will send signals that will give the team a better sense of the condition of the spacecraft.
Assuming ISEE-3 is in good health, Wingo says, the next big challenge will be to assess its trajectory for a proper thruster firing. The team will use transmitters and antennas at Arecibo, Morehead State University in Kentucky, the Bochum Observatory in Germany, and, potentially, the Allen Telescope Array in California, to ping the spacecraft. The hope is that the team will not only be able to measure Doppler shifts in frequency to get a fix on the spacecraft's velocity, but also signal time of flight to triangulate its position. This will be difficult, so even though the project met its fundraising goal on Wednesday, Wingo says the team is still seeking funds in case they must pay NASA to do the ranging for them.
The reboot project schedule is aggressive. "We’re in panic mode every day," Wingo says. "But I think we have a reasonable chance of making this work if the spacecraft is healthy."
If the effort succeeds, it won't be the first time that ISEE-3 has had a change of course. After its launch in 1978, the spacecraft was repurposed (and renamed the International Cometary Explorer) in the early 1980s to chase Halley's Comet, then tasked again with performing solar observations in 1991 before mission cancellation in 1997.
Although more capable spacecraft have since launched, recapturing ISEE-3 could give researchers access to a consistent set of instruments with which to compare old measurements of the Earth environment, Wingo says. The peak of this solar cycle is about half as active as the peak of solar cycle 21, which ISEE-3 observed.
"[We can use the] same set of instruments to look and see what the differences are in Earth’s magnetosphere," Wingo says. Most of ISEE-3’s science instruments could still be in good working order, Wingo says, as well as the core command components of the spacecraft, which has no microprocessor and hence no memory to corrupt.
If the team can get ISEE-3 to fire its thrusters by mid-June, the spacecraft will swing past the moon at an altitude of less than 50 kilometers on August 10. A few more engine firings could place it back at L1, where the spacecraft could potentially start collecting data by mid-September. If the plan works, Wingo says, the team hopes to have a website up where people can see the spacecraft's engineering telemetry and science data for themselves.