View Full Version : An Arrow to the Sun

2001-Dec-14, 12:45 PM
Clifford Will, in his book Was Einstein Right?, discusses an experimental test of general relativity called An Arrow to the Sun, now called Starprobe (http://www.nationalacademies.org/ssb/21fpcch6.htm) (p.105), to study the solar oblateness, as well as solar wind, magnetic field, corona, and photosphere. There is very little on the web (alta vista, google searches for "starprobe relativity"), the only mention I could find is on the National Academies of Science pages, and that mostly discusses the addition of the maser clock to the probe to study the redshift (Will, p.227).

Anyway, Will describes the trajectory, to get the probe within 4 solar radii of the Sun, as being a slingshot around Jupiter (as is also used by this solar probe in 2007 (http://www.jpl.nasa.gov/ice_fire/SP_SDT_Report.pdf)). So, apparently, it is cheaper to send the thing to Jupiter (http://www.planetscapes.com/solar/eng/jupiter.htm) first, then it is to send it directly to the Sun! Jupiter is 800 million km from the Sun, while we're only a fifth of that.

The problems with such an approach are discussed here (http://easyweb.easynet.co.uk/~portwin/ASTRA/Waverider/waverider3.html), but energy-wise, that seems to be the way to go.

<font size=-1>[Page numbers and solar tests added]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2001-12-14 07:54 ]</font>

Peter B
2001-Dec-15, 02:08 PM
Er, isn't that what NASA did with Ulysses?

2001-Dec-15, 02:33 PM
I guess if you're going to the Sun, that's the way to go. Ulysses milestones (http://ulysses-ops.jpl.esa.int/ulsfct/milestones1.html).

I don't see anything about Starprobe though.

Kaptain K
2001-Dec-15, 06:38 PM
A Jupiter fly-by is not necessary to get to the Sun. It is the most economical way to get out of the the ecliptic.

2001-Dec-16, 01:39 AM
Are you saying it is not necessarily the most economical way to get to the sun--if you don't have to get out of the ecliptic?

Donnie B.
2001-Dec-16, 03:56 PM
On 2001-12-15 20:39, GrapesOfWrath wrote:
Are you saying it is not necessarily the most economical way to get to the sun--if you don't have to get out of the ecliptic?

This is an interesting question. To get a spacecraft closer to the Sun, you have to cancel some or all of its momentum (which it inherits from Earth's orbital velocity) and let it fall -- either into a lower [solar] orbit, or all the way to the Sun (if that's your goal).

To go to Jupiter, you have to increase that [solar] orbital velocity... but you have your original momentum as a baseline to start from.

Is it more efficient to speed up, fly to Jupiter, and shed the momentum there? Or to slow down directly?

Seems to me that it's more likely the latter... especially if you use Venus to help out. But then, why didn't the mission in question use Venus to get out of the ecliptic? Perhaps the desired orbit was simply unattainable in that manner.

2001-Dec-16, 11:51 PM
Will seems to claim that Jupiter is the way to go, either way.