GLAST LAT Project Pisa 9/1/04

A.Brez 1

GLAST Large Area Telescope:GLAST Large Area Telescope:

Grid interface proposal

Alessandro BrezINFN Pisa

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope

GLAST LAT Project Pisa 9/1/04

A.Brez 2

Last failureLast failure

The last vibe test failed essentially because:1) The tolerance between screw shoulder and grid hole was

too large (~0.1mm)2) The screwed part was too short (~3mm)3) The steel shoulder damaged the Al hole

Result: the 4 corner screws were unlocked

¼” 4.95mm thread

Al

Steel screw with shoulder

¼”-3mils

Ti¼”+1mil

GLAST LAT Project Pisa 9/1/04

A.Brez 3

ProposalProposal

1) The tolerance between screw shoulder and flexure/grid hole has to be tight on long

2) The grid has to be reinforced with an insert that distributes the load on a larger diameter.

We consider the idea to have the tight tolerance by construction even on few points (3) dangerous, we can have real problems mounting all the towers (3X16 joints). The possibility to have a failure mounting one tower cannot be excluded.

In the EM tower, with a simplified coupling (cylindrical holes ¼”) we could mount the tower to the grid because there was a 0.1mm tolerance in the shoulder-hole coupling

GLAST LAT Project Pisa 9/1/04

A.Brez 4

Our conceptOur concept

To guarantee a safe and symmetric joint we propose to separate the alignment points from the joint points.

1) Mount the alignment jig to the bottom tray

2) Dry test

3) Put the inserts with epoxy

4) Align back the tower to the grid

5) Place the screws, RT cure of the adhesive

6) Final torque of the screws, alignment tool is removed

GLAST LAT Project Pisa 9/1/04

A.Brez 5

Alignment toolAlignment tool

The alignment tool is mounted on the bottom tray using the bottom tray reference holes and the M2.5 threaded holes

Reference points 3(the same reference points used for sidewall mounting)

GLAST LAT Project Pisa 9/1/04

A.Brez 6

Reference to the gridReference to the grid

On the grid there are 3 other reference holes. The pin/hole tolerance can be 20m without mounting problems (3 points)

GLAST LAT Project Pisa 9/1/04

A.Brez 7

InsertsInserts

GLAST LAT Project Pisa 9/1/04

A.Brez 8

GLAST LAT Project Pisa 9/1/04

A.Brez 9

The insertsThe inserts