FAST Labs’ Cutting-Edge R&D Gets Ideas to the Field Faster

As earlier articles on this collection have famous, JWST is parked at
Lagrange level L2. It’s some extent of gravitational equilibrium positioned about 1.5 million kilometers past Earth on a straight line between the planet and the solar. It’s a super location for JWST to watch the universe with out obstruction and with minimal orbital changes.

Being so far-off from Earth, nonetheless, signifies that knowledge has farther to journey to make it again in a single piece. It additionally means the communications subsystem must be dependable, as a result of the prospect of a restore mission being despatched to deal with an issue is, for the close to time period no less than, extremely unlikely. Given the fee and time concerned, says
Michael Menzel, the mission techniques engineer for JWST, “I would not encourage a rendezvous and servicing mission unless something went wildly wrong.”

According to Menzel, who has labored on JWST in some capability for over 20 years, the plan has all the time been to make use of well-understood Okay
_a-band frequencies for the cumbersome transmissions of scientific knowledge. Specifically, JWST is transmitting knowledge again to Earth on a 25.9-gigahertz channel at as much as 28 megabits per second. The Okay_a-band is a portion of the broader Okay-band (one other portion, the Ku-band, was additionally thought of).

The Lagrange factors are equilibrium places the place competing gravitational tugs on an object internet out to zero. JWST is one in all three craft at the moment occupying L2 (Shown right here at an exaggerated distance from Earth). IEEE Spectrum

Both the data-collection and transmission charges of JWST dwarf these of the older
Hubble Space Telescope. Compared to Hubble, which remains to be energetic and generates 1 to 2 gigabytes of knowledge each day, JWST can produce as much as 57 GB every day (though that quantity depends on what observations are scheduled).

Menzel says he first noticed the frequency choice proposals for JWST round 2000, when he was working at
Northrop Grumman. He turned the mission techniques engineer in 2004. “I knew where the risks were in this mission. And I wanted to make sure that we didn’t get any new risks,” he says.

IEEE Spectrum

Besides, Okay
_a-band frequencies can transmit extra knowledge than X-band (7 to 11.2 GHz) or S-band (2 to 4 GHz), frequent selections for craft in deep area. A excessive knowledge price is a necessity for the scientific work JWST can be enterprise. In addition, in keeping with Carl Hansen, a flight techniques engineer on the Space Telescope Science Institute (the science operations heart for JWST), a comparable X-band antenna could be so massive that the spacecraft would have hassle remaining regular for imaging.

Although the 25.9-GHz Okay
_a-band frequency is the telescope’s workhorse communication channel, it additionally employs two channels within the S-band. One is the two.09-GHz uplink that ferries future transmission and scientific remark schedules to the telescope at 16 kilobits per second. The different is the two.27-GHz, 40-kb/s downlink over which the telescope transmits engineering knowledge—together with its operational standing, techniques well being, and different info in regards to the telescope’s day-to-day actions.

Any scientific knowledge the JWST collects throughout its lifetime will have to be saved on board, as a result of the spacecraft doesn’t preserve round the clock contact with Earth. Data gathered from its scientific devices, as soon as collected, is saved inside the spacecraft’s 68-GB solid-state drive (3 p.c is reserved for engineering and telemetry knowledge).
Alex Hunter, additionally a flight techniques engineer on the Space Telescope Science Institute, says that by the tip of JWST’s 10-year mission life, they anticipate to be all the way down to about 60 GB due to deep-space radiation and put on and tear.

The onboard storage is sufficient to acquire knowledge for about 24 hours earlier than it runs out of room. Well earlier than that turns into a problem, JWST could have scheduled alternatives to beam that invaluable knowledge to Earth.

JWST will keep related by way of the
Deep Space Network (DSN)—a useful resource it shares with the Parker Solar Probe, Transiting Exoplanet Survey Satellite, the Voyager probes, and the complete ensemble of Mars rovers and orbiters, to call just some of the opposite heavyweights. The DSN consists of three antenna complexes: Canberra, Australia; Madrid, Spain; and Barstow, Calif. JWST must share finite antenna time with loads of different deep-space missions, every with distinctive communications wants and schedules.

IEEE Spectrum

Sandy Kwan, a DSN techniques engineer, says that contact home windows with spacecraft are scheduled 12 to twenty weeks prematurely. JWST had a higher variety of scheduled contact home windows throughout its commissioning part, as devices had been introduced on line, checked, and calibrated. Most of that course of required real-time communication with Earth.

All of the communications channels use the
Reed-Solomonerror-correction protocol—the identical error-correction normal as utilized in DVDs and Blu-ray discs in addition to QR codes. The decrease data-rate S-band channels use binary phase-shift key modulation—involving part shifting of a sign’s provider wave. The Okay-band channel, nonetheless, makes use of a quadrature phase-shift key modulation. Quadrature phase-shift keying can double a channel’s knowledge price, at the price of extra difficult transmitters and receivers.

JWST’s communications with Earth incorporate an acknowledgement protocol—solely after the JWST will get affirmation {that a} file has been efficiently obtained will it go forward and delete its copy of the info to clear up area.

The communications subsystem was assembled together with the remainder of the spacecraft bus by
Northrop Grumman, utilizing off-the-shelf parts sourced from a number of producers.

JWST has had a protracted and
often-delayed growth, however its communications system has all the time been a bedrock for the remainder of the challenge. Keeping no less than one system reliable means it’s one much less factor to fret about. Menzel can bear in mind, as an illustration, concepts for laser-based optical techniques that had been invariably rejected. “I can count at least two times where I had been approached by people who wanted to experiment with optical communications,” says Menzel. “Each time they came to me, I sent them away with the old ‘Thank you, but I don’t need it. And I don’t want it.’”