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Establishment and Observation of Space Debris Laser Ranging

Zhang Zhongping, Zhang Haifeng, Wu Zhibo, Li Pu, Meng Wendong, Chen Juping, Chen WanZhen Shanghai Observatory, Chinese Academy of Sciences


Contents:
Introduction Establishment of laser ranging to space debris system Observation results Summary


Introduction
Large amount of space debris around the earth currently. Increasing the probability of collision accident between the space targets. Become a major problem for nations which are active in space. Need kinds of methods for high precise measurement and accurate catalogue for space debris to protect against debris collision.


Introduction
China, one of the members of the IADC (InterAgency Space Debris Coordination Committee) has paid great attention to reduce possible damage from space debris. Laser ranging (LR) is a kind of real-time measuring technology with meter or sub-meter precision for space-debris observation. With the support of National Projects, Shanghai Observatory firstly in China began to research on the LR technology to space debris from 2006.


Establishment of laser ranging to space debris system
Key techniques were investigated and modifications implemented based on the 60cm SLR system at Shanghai Observatory in 2006-2008.

60cm SLR telescope


Modifications:

Establishment of laser ranging to space debris system

­ 40W laser ­ Rebuilding the laser coude system and transmitting telescope ­ Improvement of photon detector, control system, tracking system etc. Preliminary laser ranging system was constructed in 2008.

Laser Beam Performance: Frequency20Hz Energy 2J Pulse width10ns

40W Laser


(a) The discarded Soviet
rocket (ID: 17912) on July, 2008;

Preliminary Results

(b) The discarded US
rocket (ID: 30778) on July 17/18, 2008

The range variations for each pass

The maximum range obtained in the measurement was 936 km.


Establishment of laser ranging to space debris system
For further studying laser ranging to space debris technology, we have been upgrading our laser measuring system in 2009-2010, including:
adopting stable high power laser improving the capability of servo-tracking system Multi step range gate adjusting automatically adopting Two Line Elements (TLE) predict orbit , its precision <1km


Performances of stable high power Laser
Repetition rate: 10Hz Diverge: 0.5mrad Wavelength: 532nm Continuous working time Energy: 1J per shot Pulse width: 8ns Laser diameter: 13mm >1hour


Azimuth

Improvement of tracking capability

Elevation

Tracking RMS is less than 2


Some of the measuring results from the 10W laser in 2010 Successfully measuring passes is low (<20%)


Establishment of laser ranging to space debris system
Based on the 10W laser observation system, the following modifications have been done to further increase the ability of laser tracking for space debris in 2011: Laser power enlarging Automation improving
CCD closed tracking Calculation of Laser beam point for adjustment automatically


Laser power enlarging
Adapting 10W Laser Fundamental laser (1064nm) as input of amplifier. Four-stage amplifier Performances: Power : 30-35W Divergence: 15" Wavelength: 532nm Repetition rate: 10Hz


Laser power enlarging

10W laser Amplifier

30W laser beam


Automation improving
Large time bias and range bias for prediction of space debris target. The during time of passes for space debris (LEO) through the station is short (less than 6 min). Automation will improve the efficiency of search greatly. CCD closed tracking calculation of laser beam point for adjustment automatically


CCD closed tracking
Calculating the centre of target image. Getting the offset between the centre and Reference position. Sending the offset value to tracking control software. Tracking RMS is less th a n 2
Center of image


Calculation of laser beam point
Dividing the image of laser beam into two parts by the line, top borderline and bottom borderline. Least square fitting all pixels of the borderline. The intersection of two lines is the laser beam point. According to the laser beam point to adjust its direction


Observation results


Number 1 2 3 4 5 6 7 8 9 10 11

Date 2011-09-14 2011-09-14 2011-09-14 2011-09-15 2011-09-15 2011-09-15 2011-09-15 2011-09-15 2011-09-15 2011-09-15 2011-09-15

Objects 20453 16612 17291 23705 18749 20453 25263 20433 21610 23343 24969

Time (UTC) 11:09:57~ 11:13:49 11:19:44~ 11:22:33 11:29:05~ 11:29:56 10:59:18~ 11:03:48 11:34:34~ 11:35:43 11:49:38~ 11:51:24 12:11:25~ 12:12:15 20:07:50~ 20:10:36 20:29:22~ 20:30:32 19:57:28~ 9:59:43 20:14:27~ 20:15:08

Perigee/km 947 632 956 853 638 947 779 804 763 649 779

Apogee/km 427 609 940 832 609 427 776 745 758 640 776

RCS/m2 7 .0 6 4 .1 4 3 .7 4 1 0 .0 4 .6 4 7 .0 6 6 .2 4 6 .6 6 1 4 .1 7 1 2 .2 6 4 .5 8

Ranging 752~1114 6 8 2 ~1 5 8 0 1 2 3 8 ~1 4 8 6 9 8 6 ~1 3 9 3 8 5 2 ~1 2 3 9 9 0 0 ~8 4 7 8 4 0 ~9 2 8 1159~891 1106~1104 7 7 0 ~1 0 5 8 1 3 2 4 ~1 4 6 5

Returns 249 479 51 481 85 227 25 160 44 243 47


The operators have decreased (4 person before) during the measurement. The 8 passes were obtained during one night ( only 2 passes in 2010). Have the capability to track space debris target up to 1800km. The successfully measuring passes of the space debris by our laser ranging system is about 50%.


Utilization of high power laser at the frequency of 200-500Hz and Low Dark Noise Detector
The new laser system of diode pumped, 50-60W,200-500Hz, less than 10ns pulse width will be utilized to observe space debris in near future. The low dark noise and high QE detector, APD, will also be used for inaccurate predicts of space debris.
Photon detection efficiency vs. wavelength of APD


Summary
The laser returns from the space debris have been obtained firstly at the Shanghai SLR Station in July 2008. After years of system updating, the ability of laser ranging to space debris is being advanced and the numbers of measured passes are increased. As the development of laser ranging technology for space debris, some further improvements of measuring system need to be implemented in the further. The new high power laser system and lower noise detector, among the improvements, will be performed in the future to further enhance the ability of measuring system.