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Space Physics. Peter Fisher. Working in space - getting there is half the fun Experiments Just plain cool - the Tethered Satellite A long march - Gravity Probe B “Somebody’s gotta do it” - Alpha Magnetic Spectrometer Looking for a jerk - SNAP. Three big problems in space The ride uphill

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space physics

Space Physics

Peter Fisher

Peter Fisher - MIT

slide2

Working in space - getting there is half the fun

  • Experiments
    • Just plain cool - the Tethered Satellite
    • A long march - Gravity Probe B
    • “Somebody’s gotta do it” - Alpha Magnetic Spectrometer
    • Looking for a jerk - SNAP

Peter Fisher - MIT

slide3

Three big problems in space

  • The ride uphill
  • Keeping cool
  • Telemetry

Peter Fisher - MIT

slide4

Rocket equations:

The ride uphill

Vesc=8,000 m/s 31 MJ per kg into orbit

  • Consequences:
  • Must minimize mass
  • High thrust: high vibration environment
  • Reduce drag: small payload

Peter Fisher - MIT

slide5

Pegasus (Orbital Sciences)

Space shuttle

Aerobee (USAF)

Sea Launch (Boeing)

Supergun (US Army)

Delta IV (Boeing)

Peter Fisher - MIT

slide6
Delta IV Rocket

12,757 kg to orbit

1.5 m diameter shroud

~$3,000/kg

No crew

No repair, deployment

Lower safety req.

Frequent launch

Space Shuttle

29,000 kg to LEO

2.8 m diameter payload bay

~$5,000/kg

Crew

Repair, deployment

Very high safety

Grounded!

Access to ISS, or 14 day mission

Peter Fisher - MIT

slide7

Keeping cool - a question:

Shuttle:

7 crew @ 100 W each

Avionics - 2000 W

How do you get rid of waste heat in space?

Peter Fisher - MIT

slide8

Stephan-Boltzmann:

  • Prad=(57nW/m2-K4)T4
  • 461 W/m2 @ 300K
  • Solar cells:
  • Efficiency: 10-20%
  • Solar constant: 1.4kW/m2
  • Pcell=140-280W/m2

Peter Fisher - MIT

slide9

To keep cool:

  • Need 1 m2 of radiator for every 2 m2 of solar cells
  • Thermal management
  • system
  • Limit power

Radiator with freon loop

Peter Fisher - MIT

slide10

Telemetry

Space experiments always assume that communications may be lost (“comm-out”) at any time for an unknown duration.

In typical orbits, there are frequently comm-out factors of 10 (Shuttle)-40(ISS)%

Major implications…

Peter Fisher - MIT

slide11

Minimize data transmission, maximize on-board processing (subject to weight, power, thermal, etc.) 2Mb/sec. ave.

All systems must go into safe mode during comm-out

  • 3. Find an alternate data path
  • 4. On-broad storage

Peter Fisher - MIT

slide12

AMS DAQ:

600 processors, 2kW

ISS High Rate Coverage: 60%,

Removable disks inside

Peter Fisher - MIT

slide13

B

Just plain cool: the Tethered Satellite System: Concept

A conductor moving through a magnetic field generates a potential

V=El=F/q=vB/c

Between the ends.

For low Earth orbit:

v=8,000 m/s

B=0.3G

l=20 km

v

V,l

E=8mV/m

V=4,800V

Peter Fisher - MIT

slide14

B

je

je

je

je

Can generate EMF if

There is a current return path (space plasma

Magnet flux changes (orbit through dipole)

Naïve calculation:

EMF=(1/c)(dF/dt)=(1/c)A(dB/dt)

~(20 km)2(0.3 G/1000 sec.)/c

~12 V

Space plasma plays a role; Parker-Murphy theory

v

V,l

Peter Fisher - MIT

slide15

Thethered Satellite System (TSS-1) - NASA/ASI joint project

Deployable satellite with 5N thruster at the end of 20 km conducting tether deployed perpendicular to magnetic field.

Generate power, measure space plasma properties.

Peter Fisher - MIT

slide16

TSS-1: jammed after deploying 300m

TSS-1R: tether broke after 19.7 km, was generating 300W at time of separation.

Feasible method of power generation, extracts energy kinetic energy of orbiter.

Orbit lifetime> 1My.

Peter Fisher - MIT

slide17

A long march - Gravity Probe B

The Lense-Thirring effect (1918)

Rotating mass gives rise to “gravitomagnetic” field

and

  • An object with angular momentum l will precess at rate
  • a- semi-major axis of orbit
  • e - eccentricity

Peter Fisher - MIT

slide18

To measure frame dragging, need

  • Gyroscope system (provides l)
  • A way of measuring precession
  • Apparatus in orbit around large mass (Earth)
  • Gravity Probe B (1974)
  • Four high precision spheres on two axis act as gryoscopes
  • Gyros coupled to freely floating telescope, measure deflection from a target star during orbit around Earth (3 y).

Peter Fisher - MIT

slide19

Pilot study starts in 1964

  • Launch on 20 April 2004
  • Instrument checkout complete, 20 July 2004. Science starts!

http://gravityprobeb.com

Peter Fisher - MIT

somebody s gotta do it ams
“Somebody’s gotta do it” - AMS
  • Fritz Zwicky (1933): Galactic dynamics
  • Rotation curves
  • Cluster infall velocities
  • Perpendicular velocities
  • Lensing
  • By “Dark Matter”, I mean
  • g=0.15-0.60 GeV/cm3
  • No strong or EM interactions
  • Vave=250 km/s

Peter Fisher - MIT

slide22

50 GeV

Peter Fisher - MIT

slide23

Integrated positron signal above 8 GeV for 10 GeV (solid line) and 30 GeV (dotted line). The Earth is located at 8.5 kpc radius.

Peter Fisher - MIT

slide25

Magnetic turbulence - average variation of magnetic field:

Mean time between scattering from inhomogenieties:

Peter Fisher - MIT

slide26

30 GeV electron: v=c, gives average velocity along field c/31/2

Electron lifetime determined by time to to propagate one Xo=65 g/cm2 in hydrogen

1 proton/cm3 in ISM Xo=1.3 x 1013 kpc

to=45 My

Peter Fisher - MIT

slide27

Number of scatterings: N=to/ts

Random walk diffusion distance

Diffusion coefficient

Advance each step

RMS number of steps

Peter Fisher - MIT

slide28

Charged particle spectrometers

In ~10 GeV region:

p:e-:e+

103:10:0.1

p:p

103:0.1

High Energy Antimatter Telescope (Balloon)

AMS-02

Peter Fisher - MIT

slide30

AMS-02 will just nail this

Questions

Why use e+/e++e-? Solar modulation not important above 10 GeV.

Same signal appears in e-, so why not use e+, e-,… in combined fit?

AMS-01 took LOTS of e- data (easy to ID, no p!) Why not look at that?

Peter Fisher - MIT

slide31

First glance at AMS-01 data (backgrounds, resolution not well understood yet). Need to do a lot of work (Gian-Paolo, Gray)

Peter Fisher - MIT

slide32

Bumps and Bangs:

Terrestrial and solar capture

Peter Fisher - MIT

slide33

E

nDM

E-DE

Maximum when =1, E=DE

Most efficient energy transfer

Peter Fisher - MIT

slide34

24Mg

28Si

32S

16O

56Fe, 58Ni

Capture rate for Earth

Peter Fisher - MIT

slide35

Capture rate for Sun is ~108 times higher.

Since Sun is mostly protons, no peaks and no strong suppression for Majorana type DM

Earth

Sun (scaled by 5 108

Peter Fisher - MIT

slide36

Signal is SM neutrino flux from

  • The sun
  • The Earth
  • The center of the galaxy

Detectors: SuperK (Kate, last week), AMANDA, ICECubed (Jody, Feb.), ANTERES

Peter Fisher - MIT

slide37

g

M2

+

M2

g

gB

gq

Peter Fisher - MIT

slide38

Looking for jerks - SuperNova Acceleration Probe (SNAP)

Type Ia SN may be calibrated so the brightness is known independently of the distance from Earth.

The large scale structure of the universe may be determined by plotting redshift vs. magnitude (distance).

Peter Fisher - MIT

slide39

Ho = Hubble expansion parameter

qo=acceleration parameter

jo=jerk parameter

qo and jo depend on the matter content of the universe

Peter Fisher - MIT

slide42

The difficulty lies in finding the supernova early on.

Need to measure the light output in several spectral bands as a function of time. Typically, use a survey telescope to find the SN, a spectrograph to measure z and a high resolution telescope to measure light output as a function of time.

The major argument is whether this is an artisinal or industrial endeavor.

Peter Fisher - MIT

slide44

Other major endeavors in the coming years:

  • JWST - second generation Hubble Space Telescope, 6 m aperture
  • GLAST - gamma ray observatory, ten times EGRET, launch 2006
  • LISA - constellation of three satellites, long baseline gravity wave detection
  • OWL/AirWatch - optical sensor satellite to observe cerenkov radiation from high energy cosmic rays in Earth’s atmosphere
  • Plank - next generation of cosmic background radiation measurement, <1o resolution, polarization, 2009

Peter Fisher - MIT

slide45

Summary

  • Space provides access to fundamental cosmological (SN, CMB) and astrophysical (charged cosmic rays, gamma rays, neutrinos) which impact particle physics. Space is a very challenging place to try to mount an experiment:
  • Extreme engineering
  • Extreme political considerations (c.f. Presidential speech of Jan. 14, 2004)

Peter Fisher - MIT