ASTROD and ASTROD I: Progress Report

1
ASTROD and ASTROD I Progress Report
Max-Planck, Gårching Albrecht
Rüdiger Technical U, Dresden Sergei Klioner
Soffel IAA, RAS George Krasinsky Elena
Pitjeva
Imperial College Henrique Araújo Diana
Shaul Timothy Sumner CERGA J-F Mangin
Étienne Samain ONERA Pierre Touboul
ZARM, Bremen Hansjörg Dittus Claus
Lämmerzahl Stephan Theil Humboldt U, Berlin
Achim Peters U Düsseldorf Stephan Schiller
Andreas Wicht
Purple Mountain Obs, CAS Wei-Tou Ni A.
Pulido Patón J. Shi C.-F. Tong F. Wang
Y. Xia Jun Yan
Nanjing N U, X. Wu, C. Xu Huazhong S T U
Ze-Bing Zhou  Purple Mountain Obs, CAS Gang
Bao Guangyu Li Lei Liu H-Y Li
Yunnan Obs, NAOC, CAS Y.Xiong ITP, CAS,
Y-Z Zhang U Missouri-Columbia Sergei
Kopeikin Nanyang U, Singapore H-C Yeh
Nanjing U Tianyi Huang IP, CAS Y-X Nie
Z. Wei Tsing Hua U Sachie Shiomi Nanjing A
A U H. Wang
The objectives of the ASTROD (Astrodynamical
Space Test of Relativity using Optical Devices)
mission are threefold --- to discover and explore
fundamental physical laws governing matter, space
and time via testing relativistic gravity with
3-5 orders of magnitude improvement, to improve
measurement of the solar-system parameters and to
detect and observe gravitational waves from
massive black holes and galactic binary stars in
the frequency range 50 µHz to 5 mHz. A desirable
implementation is to have two spacecraft in
separate solar orbit carrying a payload of a
proof mass, two telescopes, two 1-2 W lasers, a
clock and a drag-free system, together with a
similar L1/L2 spacecraft. The 3 spacecraft range
coherently with each other using lasers.
ASTROD I with one spacecraft ranging optically
with ground stations is a first step for a full
ASTROD (Astrodynamical Space Test of Relativity
using Optical Devices) mission. The goals are
testing relativity with gamma measured to 10-7,
measuring solar-system parameters more precisely
and improving the present-day sensitivity for
gravitational wave detection using Doppler
tracking by radio waves. The spacecraft is to be
launched into an inner solar orbit with initial
period about 290 days to encounter Venus twice to
receive gravity-assistance for achieving shorter
period (165 days or less) for a sooner
measurement of Shapiro time delay.  In this
paper, we report on the progress since AMALDI5
for ASTROD and ASTROD I. Orbit motion of the 3
spacecraft of ASTROD around the Sun gives
different modulation for a gravitational-wave
signal and a solar g-mode signal. Reachable
low-frequency-end sensitivity is discussed. For
ASTROD I, we present the orbit design and orbit
simulation, preliminary accelerometer development
result, one-way transmit-receive-timing
instrumental development, and ground laser
station development. We discuss the atmosphere
transmission noise., In Poster 6timing noise,
spacecraft environmental noise, test-mass sensor
back-action, and test mass-spacecraft
control-loop noise and stiffness. Low-frequency
noise in acceleration are emphasized. Their
effects on position are discussed.
ASTROD
ASTROD I
ASTROD I Orbit 2 encounters with Venus to swing
the spacecraft to the other side of the Sun to
conduct Shapiro time delay measurement and to
measure Venus multiple moments. An orbit design
for a 2012 launch is as follows
S/C 2
ASTROD
S/C 1
Laser Ranging
Inner Orbit
Sun
Launch Position
Outer Orbit
Earth Orbit
.
L1 point

• Schematic Diagram of the Mini-ASTROD Spacecraft
• Cylindrical spacecraft with diameter 2.5m, height
  2m and surface covered with solar panels,
• (ii) In orbit, the cylindrical axis is
  perpendicular to the orbit plane with the
  telescope pointing toward the ground laser
  station. The effective area to receive sunlight
  is about 5m2 and can generate over 500W of power.
• (iii) The total mass of spacecraft is 300-350 kg.
  That of payload is 100-120 kg.
• (iv) Science data rate is 500 bps. The telemetry
  rate is 5 kbps for about 9 hours in two days.

Earth (800 days after launch)
100 fW
For weaklight phase-locking, please see poster
62.
A simulation of the accuracy for determining the
relativistic parameters ß and ?, and the solar
quadrupole parameter J2 gives 10-7, 10-7 and
10-8 for their uncertainty ?ß and ??, and ?J2.
In this simulation, we assume a 10 ps timing
accuracy and 10-13 ms-2Hz-1/2 inertial
sensor/accelerometer noise. 10 ps timing is
already achieved in satellite laser ranging. The
accelerometer requirement as compared with LISA
is shown in Poster 78..
The gravitational-wave sensitivity curve of
ASTROD and the strength of various sources. The
sensitivity is for 1 yr observation with S/N5.
Christensen-Daalsgard (2002)
See Poster 1
Both ASTROD and LISA respond to solar
oscillations. The time constants for solar
oscillations are long --- over 106 yr for low-l
g-mode oscillations and over 2-3 months for low-l
p-mode oscillations. The distance to the Sun of
the inner ASTROD spacecraft varies from 0.77 AU
to 1 AU and that of the outer ASTROD spacecraft
varies from 1 AU to 1.32 AU. When the spacecraft
move in solar orbits, the amplitude and direction
of the solar oscillation signals receive deep
modulations in addition to the modulations due to
spacecraft motion and orientation. The time
constant for the gravitational radiation (or
orbit evolution) of the close white dwarf
binaries (CWDB) is more than 106 yr, and hence
the CWDB confusion background is steady in the
inertial space. This background is modulated
only by the orientations and motions of
spacecraft, not by the distances and orientations
of the spacecraft relative to the Sun. With this
extra modulation --- deep in magnitude and
direction, the detectability of the solar
oscillation signals (hence the separability with
G-waves) reaches at least 5 orders lower than the
confusion limit in energy, i.e., to the
instrumental noise floor.
Welcome to the 3rd ASTROD Symposium Beijing,
July 16-23, 2006 (1st, Beijing, Sept. 21-23,
2001 2nd, Bremen, June 2-3, 2004)
wtni_at_pmo.ac.cn
6th Edoardo Amaldi Conference on
gravitational waves, June 20-24, 2005 Bankoku
Shinryoukan, Kise Nago
See also Poster 66