SPIDER . . .

Black Magic

UMBRAS is a a free flying occulter spacecraft that would fly in formation with a space telescope. Its primary function is to block star light from reaching the telescope, thus allowing imaging of faint objects near bright ones, such as planets about stars.

The UMBRAS spacecraft will be semi-autonomous, with its own propulsion (XIPS) and power generation (solar cells), communications, and navigation capability. We call the craft a Solar Powered Ion Driven Eclipsing Rover (SPIDER). The SPIDER would consist of several main structures:

occulting screen
sun shade
spacecraft bus
solar arrays
propulsion module(s)

The occulting screen obliquely faces the telescope, hiding the spacecraft bus and other structures from view. The sun shade, attached to the edge of the screen pointing toward the Sun, shields the screen from direct sunlight. The two spacecraft (SPIDER and the telescope) match velocities allowing the SPIDER to occult a specific target for the telescope.

The SPIDER, like any spacecraft, carries a payload: an occulting screen. This payload performs several functions:

Blocks starlight.
Hides the SPIDER spacecraft from the telescope.
Minimizes sunlight reflected toward the telescope.

The occulter moves to place the telescope in the umbra of the occulting screen with respect to the star. This is not the only umbra which is important to the functioning of the technique, as we will see.

A plan diagram (above, right) shows the SPIDER in its observing configuration with the screen erected to hide the spacecraft bus from view by the telescope.

View of N-class occulter from starward side of screen. Note in the right-most view the structure perched atop the occulting screen--the sun shade. This device allows the screen to remain dark during observations. With the sun in the plane of the occulting screen, the shade prevents sunlight from falling on the side of the screen facing the telescope. The shaded screen is darker than any otherwise illuminated material surface (bottom left view).

Meanwhile, on the other side of the screen, the solar arrays collect light to power spacecraft subsystems, while they and the rest of the spacecraft hide from telescopic view.

Our graphic artist, Edward Rowles, has produced a 3-D computer model of the basic N-class UMBRAS. Check them out to get a feel for what the vehicle looks like in the observing configuration.