JWST position vs time

[Richard D. Saam]

As JWST approached the L2 position its time(sec) and position(within .1
km) relative to the sun and earth were presented on the NASA website:

https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

The JWST time and position are not presented on this website since its
arrival at L2.

Understanding that JWST is in a quasi orbit around L2, does anyone know
if NASA (or anyone else) presents the JWST time and distance from sun
and earth as it meanders in L2?

Richard D Saam

[Lou]

I've read that although it's theoretically possible to place JWST into a
stable L2 orbit. It's like trying to balance a pin on a
table...practically, it's impossible. Not least because of perturbations
from moon, solar wind, effects from other planets, oblateness of planets
and sun etc. So if I remember correctly NASA does something like this:
They put it into a slightly incorrect but stable path pointing towards
the theoretical L2 orbit. And correct it when it starts to veer off,
with small bursts of its onboard thrusters. Which is why JWST has its
limited lifespan of only a few years. Which may be why NASA doesn't
supply any of the details you ask for. It doesn't have them.

I believe its thruster fuel runs out in about a decade.

[Martin Brown]

L1 L2 & L3 which sit on a line with the Earth-Sun axis are all
intrinsically unstable orbits. NASA reckons around 23 days before it
meanders away. Tiny errors can grow exponentially. Not helped at all for
the Earth Sun system of course by the moon being present.

L4 & L5 are truly stable synchronous orbits as the Trojan asteroids of
Jupiter clearly demonstrate (and some dust in the Earths orbit).

NASA has to actively maintain satellites on station at L1 or L2.

https://solarsystem.nasa.gov/resources/754/what-is-a-lagrange-point/

Slightly more detail on the Lagrange stability conditions with equations
here:

https://map.gsfc.nasa.gov/ContentMedia/lagrange.pdf

--
Regards,
Martin Brown

[Jonathan Thornburg [remove -color to reply]]

Lou <noeltu...@live.co.uk> wrote:
> I've read that although it's theoretically possible to place JWST into a
> stable L2 orbit. It's like trying to balance a pin on a
> table...practically, it's impossible. Not least because of perturbations
> from moon, solar wind, effects from other planets, oblateness of planets
> and sun etc. So if I remember correctly NASA does something like this:
> They put it into a slightly incorrect but stable path pointing towards
> the theoretical L2 orbit. And correct it when it starts to veer off,
> with small bursts of its onboard thrusters. Which is why JWST has its
> limited lifespan of only a few years.

Another reason why it's much better for JWST to be in an orbit around L2
rather than precisely at L2 is to avoid partial eclipses of the Sun by
the Earth -- JWST strongly benefits from a *stable* thermal environment.
(Having steady sunlight on solar panels for electrical power is also
useful.)

For a bit more on these "Halo" orbits, see
https://en.wikipedia.org/wiki/Lagrange_points#Sun%E2%80%93Earth
https://en.wikipedia.org/wiki/Halo_orbit

--
-- "Jonathan Thornburg [remove -color to reply]" <jthor...@gmail-pink.com>
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
currently on the west coast of Canada
"C++ is to programming as sex is to reproduction. Better ways might
technically exist but they're not nearly as much fun." -- Nikolai Irgens
"that applies to Perl, too!" -- me

[Richard D. Saam]

JWST sun and earth L2 positions (within 1 km)
are presented at skylive.com.
The JWST, with its large thermal insulation surface area,
should respond to the solar wind dynamic character.
More accurate JWST positional data with time would
be a data source for analyzing the solar wind dynamics.
The Deep Space Network probably controls
the significant digits(.1, .01 or maybe .001 km) here.
I would like to have access to such.

Richard D Saam

[Richard D. Saam]

On 4/5/22 2:57 PM, Richard D. Saam wrote:
> On 3/22/22 6:31 AM, Lou wrote:
>> On Monday, 14 March 2022 at 20:47:39 UTC, Richard D. Saam wrote:

>> I've read that although it's theoretically possible to place JWST into a
>> stable L2 orbit. It's like trying to balance a pin on a
>> table...practically, it's impossible. Not least because of perturbations
>> from moon, solar wind, effects from other planets, oblateness of planets
>> and sun etc. So if I remember correctly NASA does something like this:
>> They put it into a slightly incorrect but stable path pointing towards
>> the theoretical L2 orbit. And correct it when it starts to veer off,
>> with small bursts of its onboard thrusters. Which is why JWST has its
>> limited lifespan of only a few years. Which may be why NASA doesn't
>> supply any of the details you ask for. It doesn't have them.
>>
>> I believe its thruster fuel runs out in about a decade.
>>
> JWST sun and earth L2 positions (within 1 km)
> are presented at skylive.com.
> The JWST, with its large thermal insulation surface area,
> should respond to the solar wind dynamic character.
> More accurate JWST positional data with time would
> be a data source for analyzing the solar wind dynamics.
> The Deep Space Network probably controls
> the significant digits(.1, .01 or maybe .001 km) here.
> I would like to have access to such.
>
> Richard D Saam
>

As a followup, the JWST ephemeris is available at:
https://ssd.jpl.nasa.gov/horizons/app.html#/