Where is Webb?

[BlackBart]

Some discussion of the Webb space telescope in another thread, but here's a spot just to talk about this amazing project.

https://webb.nasa.gov/content/webbLaunc ... sWebb.html

Check the link above regularly to see which bit is unfolding every day, and where it is, and how fast it's going. Today one set of the mirrors are unfolding and moving into place. As of today it is about 72% of the distance to its designated parking spot about a million miles from earth ("behind" earth from the sun). It will orbit around the sun with us, not orbit around the earth. From there it is away from the earth's gravity and dust and haze, and will look literally back into time, where it will see infrared light from some of the earliest explosions and collisions of the universe. Hard to even imagine.

It is slowing way down now, traveling about 1000 mph, "coasting" as they describe it, so that it can be slowed down with the sun's gravitational pull and maneuvering rockets. It will navigate around it's destination point in almost a bicycle wheel path so that the earth doesn't shade it's solar power panels. It has some fuel to power navigational rockets, and a coolant system so the mirrors can be kept very cold. It has sunshades the size of a tennis court to keep it out of the sun's heat.

I'm very excited about this extraordinary machine, the engineering involved, and the unprecedented information it will be able to send back.

nasa-james-webb-spae-telescope.jpg (105.69 KiB) Viewed 1616 times

james-webb-scale-80ea928.jpg (359.9 KiB) Viewed 1616 times

Here's it's route out to position "L2."

[RickHaleParker]

It is slowing way down now, traveling about 1000 mph, "coasting" as they describe it, so that it can be slowed down with the sun's gravitational pull and maneuvering rockets.

Webb is still in the Earth's gravity well. It coasting up the side of the Earth's gravity well. Same thing as costing up a hill on earth. Velocity will drop to zero just short of L2. Then they will use powered flight to insert Webb into orbit around L2.

Coasting saves fuel in space just as it does on earth. At about $10,000 per kilogram to launch mass into space. You want to save all the fuel ( mass ) you can.

[abscate]

These accomplishments require we use ALL of our talent of humankind…….

[volvolugnut]

I am amassed what was done with the much simpler tools used by early space flight.

For a peek at the NASA world at that time, see this book:
Failure Is Not an Option
Mission Control From Mercury to Apollo 13 and Beyond
By Gene Kranz

volvolugnut

[BlackBart]

Webb is still in the Earth's gravity well. It coasting up the side of the Earth's gravity well. Same thing as costing up a hill on earth. Velocity will drop to zero just short of L2. Then they will use powered flight to insert Webb into orbit around L2.

I want to try and get my head around that more. Is the current route not a straight line, but a curve around the gravitational sphere of earth? So sort of a boomerang out to L2?

And is it actually orbiting "something" (the edge of earths gravitational sphere?) at L2, or being maneuvered with thrusters? It has to be traveling the same speed around the sun as earth, but what causes it to do the bicycle loops along that path?

[RickHaleParker]

I want to try and get my head around that more. Is the current route not a straight line, but a curve around the gravitational sphere of earth? So sort of a boomerang out to L2?

And is it actually orbiting "something" (the edge of earths gravitational sphere?) at L2, or being maneuvered with thrusters? It has to be traveling the same speed around the sun as earth, but what causes it to do the bicycle loops along that path?

Gravity Well not Gravity Sphere.

The route is a straight line across warped space. Gravity warps space.

Lagrange points are like the crest of a hill. You could park your car on the crest of a hill without brakes but you could not park your car on the slope of a hill without brakes. At the crest of a hill the gravity pulling on the front of the car down one side of the hill and rear of the car down the other side of the hill are balanced. It would be a precarious balance in need of positional maintenance.

At a Lagrange points Gravity and Centrifugal force are in equilibrium but L2 is a unstable equilibrium point with no gravitational pull .. precarious balance again. An object at L2 will drift. With a little clever station positional maintenance ( thrust ) the drift can be turned into a orbit. L2 is in the Earth's shadow. Solar panels don't work without solar radiation. That is why you don't want to park dead center of L2.

[BlackBart]

“Webb will continue to travel to the second Lagrange point (L2) for another two weeks, at which point it will enter a large orbit around the L2 point. The following five months will be used to cool the telescope to operating temperature, fine-tune the mirror alignment, and calibrate the instruments.“

[BlackBart]

“The 18 primary mirror segments and secondary mirror are adjustable via six actuators that are attached to the back of each mirror. The primary mirror segments also have an additional actuator at its center that adjusts its curvature. The telescope's tertiary mirror remains stationary. The primary and secondary mirror segments will move a total of 12.5mm, in small increments, over the course of ~10 days to complete each segment's deployment.

“After all individual mirror segment deployments are completed, the detailed optical mirror alignment process begins which is about a 3 month process. In parallel, as temperatures cool enough, instrument teams will turn on their instruments and begin each instrument's commissioning process.“

[BlackBart]

Today they started moving the mirror segments up from their stowed position almost a half inch, where they will be ready for the start of the alignment process. The mirrors will move about 1mm per day over about a 10 day period.

[BlackBart]

How Lagrange points work -