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Lecture 4: Spaceflight Environment
Space Environment and Effects
1.
Gravity (see
Lecture 3):
Microgravity, Microgravity
Simulation
Launch / Landing
Acceleration
Launch / On-orbit Vibration and Microgravity Perturbation
2.
Other Space Environment
Radiation
Environment:
Radiation, Plasma, Meteoroids and Space Debris, Atomic Oxygen, Geomagnetic Effects, Contamination
Space is full of ionized radiation and solar radiation such as gamma rays, x-rays, and ultraviolet rays. The space radiation environment is composed of various types of particles. These include a radiation belt consisting of particles captured by the Earth's magnetic field and surrounding the Earth like a donut; protons with energies ranging from 10 through 1016 Mev; galactic radiation composed of many types of nuclei such as helium, carbon, oxygen, and iron; and high levels of particles generated by solar flares. Utilizing such an environment, various types of research can be conducted in the fields of life science, medicine and so on. For instance, research on the adaptability and ecology of living things in the space environments and research on physical effects of radiation on living things and mankind can be performed.
Vacuum
Environment:
Space
provides a large-scale high-level vacuum environment which can never be
obtained on the ground. The level of space vacuum depends on the altitude above
the Earth. At the ISS altitude about 400km (250mi), the pressure of the
environment is about one 100,000th of 1Pa, which is about 0ne 100 milllionth of the pressure on the ground. Utilizing the
features of this high-level vacuum and microgravity, pure materials can be
produced from the melted state with a purity which can never been realized on
the ground. High-quality semiconductors are also expected to be produced
utilizing the high- level vacuum.
Human Exposure to Space Vacuum: http://www.sff.net/people/Geoffrey.Landis/vacuum.html
Also: residual atmosphere (spacecraft offgassing / discharges / thrusters -
contamination)
http://www.corrosion-doctors.org/Space/Frames.htm
Space debris / micro-meteorites
UV and ionizing radiation (photochemical degradation), atomic oxygen (erosion),
thermal gradients between sunlight and shadow
charged and neutral particles.
3.
Spaceflight Environment
Pressurized
Carriers (NSTS, ISS):
Atmosphere:
Temperature, Humidity, Pressure, Partial Pressure (Atmosphere Composition),
Trace Contaminants
Other:
Radiation, EMI/EMC, Services: power, thermal, data/communication/video
Unpressurized Carriers (Satellites):
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For additional details, refer to the
appropriate Interface Definition Documents (IDD) for the carrier of interest:
Middeck IDD: http://shuttlepayloads.jsc.nasa.gov/data/PayloadDocs/PayloadDocs.htm
Spacehab IDD: http://www.boeing.com/nosearch/sh_verification/
From
NSTS-21000-IDD-MDK, REV B 6-1
·
Dew Point +61oF to
+39oF
·
Cabin Pressure
o
14.7 + 0.2 PSIA
(Normal Operation)
o
8.0 + 0.2 PSIA
(Abort Operations – To be considered for Structural Design Purposes. Payload
required to be powered off.)
o
16.0 PSIA Maximum
On-Orbit (Relief Valve Operation)
o
18.1 PSIA maximum
(Ground Pressurization Test)
o
Reduced cabin
pressure EVA procedure: 10.2 ± 0.5 psia (+ 0.2 PSIA dynamic operating range, ±
0.3 PSIA sensor bias error)
·
Cabin Rate of
Pressure Change
o
Nominal Ops 2.0
psi/min Repressurization/Depressurization
o
Contingency (other
than Bailout) 9.0 psi/min Depressurization/Repressurization
o
6.1.1 Emergency
Bailout Requirements: Payloads located
within the crew compartment area shall be designed to meet the following
depressurization requirements in order to insure they will not present a hazard
to the crew or to the Orbiter which could jeopardize crew survivability or
impede crew egress during emergency bailout procedures:
o
Initial (Max) 15.2
PSIA / Final (Min) 3.95 PSIA / Max Depressurization Rate 24.0 PSI/Minute
·
Cabin O2
Concentration
o
25.9 percent at
14.7 + 0.2 PSIA 30.0 percent maximum at 10.2 PSIA
o
32.0 percent at 8
psia
·
Temperature (Cabin
Air)
o
65 - 80 ºF Nominal
on-orbit operations
o
80 ºF Peak
launch/ascent
o
75 ºF Peak
entry/landing
o
95 ºF Peak
contingency operations
o
32 - 120 ºF Ferry
flight
Pressure and Atmosphere Composition (Partial Pressure)
Structural Loads proportional to pressure - reduce mass with reduced pressure.
Minimum pressure limited by partial pressure oxygen - physiological limits.
Reduced pressure limits convective heat transfer.
Partial Pressure Oxygen (O2)
Typically keep at 21-30%; Earth: 21%
Flammability (keep at less than 30%): study of oxygen effects
Physiological Requirements
Partial Pressure Carbon Dioxide (CO2)
Physiological Limits: keep below 1% = 10,000 ppm; Earth: 350 ppm
Typical levels depending on crew activity: 2,000 - 7,000 ppm (0.2 - 0.7%)
Pressure Effects: Decompression, Extra-Vehicular Activity
Reduce pressure prior to EVA to aid in reduction of dissolved N2 in blood
Emergency depressurization rates: 9 psi/min: ==> adequate venting of sealed containers
Trace Contaminants
offgassing of solvents; limited material choices / prefer metals
allowable trace contaminants listed in SMAC (Shuttle Maximum Allowable Concentrations)
each payload needs offgas test or analysis (NASA-STD-6001) (72 hrs. @120F @ambient pressure +/- 0.5 psi)
trace contaminants may be harmful to other systems but not humans (ethylene = plant hormone)
Temperature
Comfort / Crew Safety
4°C < T < 45°C for crew safety;
no exposed surfaces below dew point temperature (controlled to 63°F), otherwise condensation
Humidity
Two-Phase Fluid Handling - gas - liquid separation
Dew Point - Condensation - minimum allowable
surface temperature > dew point
Airflow / Circulation
· limited exhaust velocity - discomfort / noise
·
limited convective cooling: The ISS design value for the
convective heat transfer coefficient from the payload enclosure to the cabin
environment is 0.20 Btu/hr °F ft2 for 14.7 psia or 0.17 Btu/hr °F ft2 for
10.2-psia cabin pressure. These values shall be used in thermal
analysis/testing.
· requires cleaning of air inlet / outlet filters
Heat Rejection
· Avionics air cooling (acoustics, crew comfort, air recirculation, maximum allowable exhaust velocity)
· Water cooling (rack payloads only)
Electric Power
· typically 28 VDC, some 110 VAC / 400 Hz available; 5, 10 and 20 Amp typical. Limited number of powered payloads - heat !
· typical middeck locker experiment limited to 130 Watt: heat rejection limit
· Voltage drop across lines
· Conducted EMI: protection against 'noisy' environment needed
· Requires over-current protection devices (fuse, breaker) and adequate wire sizing
Communication
· Even with TDRS, expect LOS (loss of signal) for typically 5-30% of time (during 90 minute orbit)
· Shuttle limited to 'simple' RS232 serial data system for limited number of users
· Space Station: Ethernet communication
Video
· Analog and, more recently digital video downlink available (limited)
Electro-Magnetic Interference EMI
· conducted and radiated EMI - both emissions from payload and susceptibility to EMI from others
· typical sources: DC-DC converters, switches, Ac inverters, computers, display screens, solenoids, motors, valves