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## Space Physics

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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

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

Space shuttle

Aerobee (USAF)

Sea Launch (Boeing)

Supergun (US Army)

Delta IV (Boeing)

Peter Fisher - MIT

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

Shuttle:

7 crew @ 100 W each

Avionics - 2000 W

How do you get rid of waste heat in space?

Peter Fisher - MIT

- 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

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

Radiator with freon loop

Peter Fisher - MIT

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

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

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

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

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

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

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

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

- 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

- 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

Peter Fisher - MIT

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

Charged particles follow magnetic field lines

Peter Fisher - MIT

Magnetic turbulence - average variation of magnetic field:

Mean time between scattering from inhomogenieties:

Peter Fisher - MIT

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

Number of scatterings: N=to/ts

Random walk diffusion distance

Diffusion coefficient

Advance each step

RMS number of steps

Peter Fisher - MIT

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

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

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

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

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

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

Ho = Hubble expansion parameter

qo=acceleration parameter

jo=jerk parameter

qo and jo depend on the matter content of the universe

Peter Fisher - MIT

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

Industrial approach - orbiting observatory with all three instruments.

Peter Fisher - MIT

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

- 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

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