As earlier articles on this sequence 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 distant from Earth, nevertheless, signifies that information 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 not less than, extremely unlikely. Given the price and time concerned, says
Michael Menzel, the mission programs engineer for JWST, “I might not encourage a rendezvous and servicing mission except one thing went wildly flawed.”

Based on Menzel, who has labored on JWST in some capability for over 20 years, the plan has at all times been to make use of well-understood Okay
_a-band frequencies for the cumbersome transmissions of scientific information. Particularly, JWST is transmitting information 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 areas the place competing gravitational tugs on an object internet out to zero. JWST is one in every of three craft presently occupying L2 (Proven right here at an exaggerated distance from Earth). IEEE Spectrum

Each the data-collection and transmission charges of JWST dwarf these of the older
Hubble Area Telescope. In comparison with Hubble, which continues to be lively and generates 1 to 2 gigabytes of information day by day, JWST can produce as much as 57 GB every day (though that quantity relies 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 programs engineer in 2004. “I knew the place the dangers have been on this mission. And I needed to ensure that we didn’t get any new dangers,” he says.

IEEE Spectrum

Apart from, Okay
_a-band frequencies can transmit extra information than X-band (7 to 11.2 GHz) or S-band (2 to 4 GHz), widespread selections for craft in deep house. A excessive information price is a necessity for the scientific work JWST shall be enterprise. As well as, in line with Carl Hansen, a flight programs engineer on the Area Telescope Science Institute (the science operations middle for JWST), a comparable X-band antenna can be so giant that the spacecraft would have bother remaining regular for imaging.

Though 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 opposite is the two.27-GHz, 40-kb/s downlink over which the telescope transmits engineering information—together with its operational standing, programs well being, and different data regarding the telescope’s day-to-day actions.

Any scientific information 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. Knowledge gathered from its scientific devices, as soon as collected, is saved throughout the spacecraft’s 68-GB solid-state drive (3 p.c is reserved for engineering and telemetry information).
Alex Hunter, additionally a flight programs engineer on the Area Telescope Science Institute, says that by the top 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 gather information for about 24 hours earlier than it runs out of room. Nicely earlier than that turns into a problem, JWST could have scheduled alternatives to beam that invaluable information to Earth.

JWST will keep related through the
Deep Area Community (DSN)—a useful resource it shares with the Parker Photo voltaic Probe, Transiting Exoplanet Survey Satellite tv for pc, the Voyager probes, and the whole 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 programs engineer, says that contact home windows with spacecraft are scheduled 12 to twenty weeks upfront. JWST had a larger variety of scheduled contact home windows throughout its commissioning part, as devices have been introduced on line, checked, and calibrated. Most of that course of required real-time communication with Earth.

All the communications channels use the
Reed-Solomonerror-correction protocol—the identical error-correction customary 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, nevertheless, makes use of a quadrature phase-shift key modulation. Quadrature phase-shift keying can double a channel’s information price, at the price of extra sophisticated 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 acquired will it go forward and delete its copy of the info to clear up house.

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

JWST has had an extended and
often-delayed improvement, however its communications system has at all times been a bedrock for the remainder of the venture. Preserving not less than one system reliable means it’s one much less factor to fret about. Menzel can keep in mind, for example, concepts for laser-based optical programs that have been invariably rejected. “I can rely not less than two instances the place I had been approached by individuals who needed to experiment with optical communications,” says Menzel. “Every time they got here to me, I despatched them away with the outdated ‘Thanks, however I don’t want it. And I don’t need it.’”