Webb telescope launch date slips again

We "don't have a lot of reserve" left.

Read the whole story

 

[wagnerrp]

Even the bolts and materials are probably different.

What bolts? To save space, JWST is gluing everything!

Wasn’t there a big SNAFU a couple years back when Northrup was assembling (or reassembling) part of JWST and found they had leftover bolts at the end?

 

[wagnerrp]

Then, put it on top of a rocket - whose most recent launch was a failure - and hope for the best!

Ariane 5’s last launch was a success. It has been grounded not because it failed but out of caution from telemetry they didn’t like.

 

[wagnerrp]

The container could be loaded on C-5 and flown to Kourou Airport, which is immediately adjacent to Guiana Space Center, with the west end of the runway just hundreds of feet from the main road that heads north to the launch complex. That's how most satellites get there.

The problem is that the short little access road connecting the airport to the main road crosses a short little bridge over a canal that runs alongside the main road. That bridge is fine for the containers used for transporting large GEO comsats, but it can't support the weight of the very robust STTARS container.

The route from the wharf to the main road doesn't cross any flimsy bridges, and that's really the only reason why JWST is being delivered by sea. I'm sure the Army Corps of Engineers would have no difficulty whipping up a temporary bridge using equipment they already have that would allow STTARS to be trucked across that pesky canal as if it were an Abrams tank, but I'm also sure it's not that simple when politics are involved.

Politics (or budgets and how they can be spent) is almost certainly involved. NASA can't pay for infrastructure improvements in France. So if they wanted to fly JWST into Kourou, ESA would have to pay to fix up that bridge. I suspect that, when they were negotiating the responsibilities and budgets for the launch, they looked at what it would cost NASA to transport JWST by sea versus air, what the road work would cost ESA, and settled on transporting it by sea.

Or they could just build a new bridge, and have a newer, better bridge over which they could transfer other heavy payloads in the future.

 

[wagnerrp]

I feel like when they were dividing up the member countries contributions somebody should have pointed out that they could launch from just up the coast from it’s final construction location, and skip the whole “how are we going to ship our incredibly fragile space telescope half way across the world to launch”

So instead you want to ship a whole Ariane 5 up to Vandenburg, and build a brand new launch complex for it?

 

[wagnerrp]

Arrrr I need a hobby

Best first post ever?

 

[wagnerrp]

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter.

Is it your understanding that ion engines don't use fuel? Because I can assure you that they do.

But it’s an ion thruster. The ~7.5km/s needed to spiral out to SEL-2 only takes around 1.5t of extra propellant. The problem is going to be time, not all the extra propellant mass.

I asked about risks and your answer is basically that it's riskier without explanation. What's shifting once the sunshade is deployed and the mirror is open and locked? Nothing is.

The fuel for the ion thruster (it is a gas, but still vulnerable to sloshing). The liquid helium onboard the JWST. Both of which can create dangerous oscillations.

Then there are the much smaller but non-neglible effects of light pressure on the opened canopy.

At the extremely low acceleration of an ion thruster, why would any of that matter?

 

[wagnerrp]

The question related to sending the telescope from LEO to the LaGrange point with an ion engine. So the concern about needing more fuel is a non-starter.

Is it your understanding that ion engines don't use fuel? Because I can assure you that they do.

But it’s an ion thruster. The ~7.5km/s needed to spiral out to SEL-2 only takes around 1.5t of extra propellant. The problem is going to be time, not all the extra propellant mass.

And the current mass balance is such that they don't have an extra 1.5t to spare.

Totally false. They can’t spare another 1.5t because the Ariane 5 can’t lift that much on a transfer to SEL-2, but the Ariane 5 would only be lifting to LEO, and it can most definitely do 7.5t to LEO.