This is discussed in the article, as the sibling (Mike) comments, JWST uses the Deep Space Network (DSN) for comms.
The issue isn't so much blackout (the segments are 120 degrees separated^), but that contact time is expensive and you don't get 100% of the uptime to yourself. The DSN is basically the only infrastructure we have for this sort of long range communication. There are only three stations and JWST is sharing time with a bunch of other missions including everything that's currently on Mars. Scheduling takes place far in advance.
The problem also isn't absolute storage space onboard, even if capacity degrades at a gig a year, it's whether you can drain it faster than you fill it. That said, there is likely to be some limit on hard drive space depending on what the current rad hardened solutions are. JWST is built on very robust and well-known hardware that has good provenance in space. For a LEO mission you might be willing to risk less tolerant components to get terabytes of capacity, but out there you want extremely resilient components and 68 GB is probably the balance. Sentinel 2 (an ESA Earth observation satellite) has 2.4Tb/300GB onboard for example.
Ultimately the missions planners budget for how much data they're allowed to stream back and they've figured out an amount that is acceptable.
But in general, yes. If you can write to a disk and ship it, that's a good solution. IceCube (South Pole) generates TBs of data. We send back 0.5 TB of critical data every month over a fast satellite link, crucial alerts and telemetry are sent over Iridium (24/7 avail) and the rest gets sent back to Madison (WI) on a plane each summer.
^ In theory this means that you can service three missions at a time though, if they're not all in the same direction.
> There are only three stations and JWST is sharing time with a bunch of other missions including everything that's currently on Mars. Scheduling takes place far in advance.
There are 3 DSN complexes, but each complex has multiple dishes. One station is very frequently talking to multiple spacecraft at once.
it seems weird to spend $10billion on a telescope that lasts for 4-5 years and then not spend the money on a communication system that isn't limited by traffic and is 'expensive', or a spare drive to double its lifespan.
It's kind of important to remember that they didn't intend to spend $10B on the telescope and that it's going to last for ~20 years. The original price was expected to be $500M and it would have never been approved if the original price was $10B. It only ended up being able to get to such a cost because of gradual overruns over 20+ years and sunk cost.
That said, NASA have been expanding the DSN for the past decade with four new antennae added so far (remaining two expected by 2025), it's just slow progress as usual with most of what they do lately. DSN antennas don't bring in jobs (and thus votes) for senators the way decades long flagship projects like JWST or SLS do.
Lifespan is not dictated by hard disk space, it's dictated by consumables like liquid helium, other cryosystems and fuel for stationkeeping thrusters. Most big NASA projects are specced to just promise enough to get funded (in terms of science) and overengineered, so what gets built will often be stretched longer than the intial deliverables demanded anyway (see basically all the recent Mars rovers).
I don't think you understand how much "billions of dollars" is for construction projects. We're talking a communication system, not the large hadron collider.
Cool, that does seem like plenty of overhead even if JWST spends the bulk of its time imaging.
Reading the article further, I was sort of surprised there’s only 68 GB of solid state storage on board. Does anyone know if that’s considered very large for space-grade systems?
There are only 8 hours of downlink time per day. DSN resources are limited and shared among many missions.
Everything was sized based on the expected volume of data that the telescope would be able to take. The instruments only generatedata at a certain rate, and there are inefficiencies involved with slewing between targets. Having a larger recorder or faster downlink would not mean that JWST could take more science data.
The article mentions that there are blackout windows, I guess when the US is facing away from JWST. Only the low bandwidth DSN has coverage all the time.
0.028*3600 = 100 Gbit/hour
No problem here.