Major disasters such as Challenger or Apollo 13 had one cause, there were not several causes that led to them.
True – On both occasions, warning signals to prevent the launch were neglected.
Question 2
My receiver get 1/4th
the power of what was transmitted from Earth, how many dB is that?
P (dBW) = 10 x log10(P(W) / 1W) = 10 x log10(0.25 W / 1W) = 10 x log10(0.25)
= 10 x -0.60206 = -6.02 dB
Question 3
I want to put my satellite into a 60 degree inclination in LEO (Lower Earth Orbit). Which launch site(s) can I use?
The surface velocity of Earth’s rotation increases near the equator and reduces in the direction of the poles, hence launch sites are located near the equator to take advantage of the available boost of the Earth’s rotation.
Launching sites are also located near eastern coast line to prevent destruction of developed environment in cases of unforeseen failure of the satellite launch.
Examples of launch sites to use include Jiuquan Satellite Launch Center, China, Naro Space Center, South Jeolla, South Korea and Wallops Flight Facility, Virginia, USA
Question 4
Your team is planning an operation which has never been done before. Your team does a risk analysis off the top of their head and think that the likelihood of damaging the aircraft would be very likely and that the impact to launch ops is that you would have to slip the launch by a month. This means that you only have one launch attempt that month, and the next launch attempt would be a year later. Explain your reasoning.
(a) Where is that on the fever chart? Figure 24-9. That is, what numbers, 1-1, or 2-3, and which number is which?
The fever chart represents the level of risk depending on the probability of likelihood and impact of the situation where red shows high risk represented by 3-5, 4-4, 4-5, 5-3, 5-4, and 5-5. Yellow indicates medium risk represented by 2-3, 2-4, 2-5, 3-3, 3-4, 4-2, 4-3, 2-1, and 5-2. Lastly, green, low risk displayed by points 1-1 to 1-5, 2-1 to 4-1, and 2-2 to 2-3. In the scenario above, point A would represent the nature of the risk of the situation described by very likelihood and high impact shown in delay of undertaking of the mission.
(b) Would you allow the test assuming you are the only one who can authorize this, and all opinions have been given to you by your team?
No I would not allow to proceed with test considering the risks highlighted and significant impact of failure which could definitely cause death to the astronauts. Death cannot be reversed but the launch could be postponed. Postponement of the launch until full confidence in all operations is confirmed would be the best solution.
Question 5
You are designing a satellite which will be orbiting half way between Mercury and Venus. Your spacecraft is Bare Aluminum.
(a) Would you paint it to reject heat?
No paint would be applied to reject heat due to the high degradation of its thermo-optical properties reducing the mission reliability strength.
(b) If you do, with what paint?
Special white paints known as white ink radiators are most commonly used paint to reject heat on satellites.
(c) What is your reasoning for painting it or not painting it or covering it with something other than paint?
A good passive radiator for a thermo-optical surface requires high emissivity levels in the infrared spectrum and low absorption in the solar spectrum. The optical solar reflector (OSR) model where a layer of glass is glued to the aluminum using a qualified resin-based silicon for space is found to be the ideal instrument for thermal control of satellites exhibited by its characteristics of low degradation and higher absorption/emission ratio when matched with white ink radiators.
Question 6
The received power in a satellite digital communications link is 1.0 pW. The carrier is 8-PSK modulated at a bit rate of 2.872 Mb/s. If the noise power density at the receiver is 0.6×10-19 J, determine the bit error rate.
Bit Error Rate (BER) = ½ erfc ( X Log2
(M)
= ½ (1pW) [ x Log2
(8)] = ½
= 1 = -107.23dB
Question 7
Give two reasons why we use decibels in Space Communication instead of 10x power?
(a) Decibels are used in Space Communication due to its easy representation of very small and very large numbers within a short range of number.
(b) Decibels use two different scales depending on the nature of the quantities; Field, power, and root-power. For power quantities, the number of decibels is ten times the logarithm to base 10 of the ratio of two power quantities, that is, a change in power by a factor of 10 corresponds to a 10 dB change in level. For field quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level.
Question 8
There are two passive ADCS control techniques.
(i) What are they, and
(a) Gravity-gradient control.
(b) Spin stabilization.
(ii) How do they work?
(a) Gravity-gradient control.
Gravity gradient control uses inertia attributes of a spacecraft to stabilize it in a Nadir pointing mode, more specifically pointing towards the Earth. Inertia instants of the spacecraft are initiated by a propelled shock and then a placement influence is used to moderate the motion introduced. The propelled inertia is usually planned to be retractable to ensure efficient undertaking of the placement activity which is vital in proper settlement of the spacecraft.
(b) Spin stabilization control.
Spin stabilization control technique encompasses of a spacecraft rotating to form a stability position that will inactively decrease the effect of unsteadiness within two axis and to be unresponsive to the unsteadiness within three axis or to resolve them.
Question 9
You are in charge of all payload testing at the launch site. Three upper level engineer managers have been convinced that we need to perform a test that has never been performed before at the launch site.
(a) Would you allow it and why?
Yes I would allow it. Launch sites are for exploration operations and for three upper level engineers’ managers to collude to undertake a test? Then the test could be considered if it complies with the necessary requirements in undertaking similar tests.
(b) What difference would it make in your decision if the test took 3 hours or 43 hours? 43 hours would mean a two day launch delay, and if you didn’t make that, you would have a conflict with another launch and would have to wait another month.
The time duration of conducting the test is critical, if the time does not interfere with another already programmed launch then the test could be accepted, but if it coincides with another, then the test will have to be accepted but postponed to workable period.
Question 10
Define basic reliability vs. mission reliability.
Reliability is defined as the probability of an item to complete a distinct purpose without disappointment under specified settings for a definite period. On the other hand, mission reliability is the probability of an item to achieve predetermined objectives during a definite task undertaking. When the expected functionality time of the item matches the task duration, reliability transforms to mission reliability.
Question 11
If a spacecraft has solar panels and is always in sunlight, why does it need batteries?
Batteries are used to store energy to be used when the sunlight is not able to provide required amount of energy.
Question 12
(i) What is the difference between Amp-hour and Watt-hour?
Watt-hours is the total energy used by an equipment over a period of time associated with alternate current (AC) supply while amp-hour is a measure of a battery’s electrical current storage capability associated with direct current (DC) supply.
(ii) How much power will a 50 W-hr battery put out for 20 hours?
Power = 50W-hr x 20 hrs = 1000 W-hr = 1KW-hr
Question 13
On what kind of mission would you use an RTG and why?
RTGs are used on NASA tasks as an alternative source of power when solar and other power source options have become unworkable or unable to provide power to undertake its scientific or functioning objectives.
Question 14
Name 3 passive thermal control systems and describe how they work.
Passive thermal control systems are cooling systems used in spacecraft to control the amount of energy discharged and absorbed by use of conduction, convection and radiation to transfer the surplus heat.
(a) Heat pipes
Heat transmission is through a pipe containing a liquid where one end is connected to the heat source and the other end is connected to a heat exchanger such as a heat sink. The heat produced increases the temperature of the liquid driving the liquid to the cooling end. The liquid decreases in temperature on impact with the cooling end and reverts back to the heat source through a duct action or gravity.
(b) Heat Sinks
Heat sinks transfer additional heat through using insulation on the heat source such as aluminum and copper. Through conduction, heat is transferred from the heat source to the insulation where the heat emits from the insulation which is the heat sink to air through convection. Some heat sinks incorporate fin-like structures on its base to increase existing surface area for convection and radiation.
(c) . Heat spreaders
Heat spreaders are conductive materials used as intermediaries between a heat source and a heat exchanger to enhance the distribution of the heat to the heat exchanger. Heat spreaders may be integrated onto the heat source to increase efficiency of emitting the excess heat through the heat sink.
Question 15
Name 3 active thermal control systems and describe how they work.
Active thermal controls systems are more efficient than passive thermal control systems as they use external energy to transfer heat from the heat source.
(a) Forced air
Forced air entails using equipment such as fans and blowers, to increase the flow of air directly to a heat source dispersing heated air and thus reducing the temperature of the heat source. Proper positioning of the external influence is critical in augmenting the cooling system.
(b) Forced liquid
Forced liquid encompasses of a closed loop system which uses a pump to transfer heat through a cooling liquid moving from the heat source to a secondary heat exchanger. The heated liquid is cooled at the heat exchanger plate and transferred back to the heat source and the cycle is repeated.
(c) Solid-state heat pumps
These are semi-conductors placed between the heat source and heat exchanger to enhance heat emission through conduction. The increase in temperature on the semi-conductors, forms a temperature variance between the two sides of the conductor and smoothens heat transfer from the heat source to the exchanger.
Question 16
MLI has many layers of reflectors?
The number of layers is influenced by the anticipated heat transfer required but for long-term low earth orbit spacecraft, 15 - 20 reflector layers are used (Dooling " Finckenor 1999, p. 11).
Between each is a separator layer.
(a) What is the function of the separator layer?
To ensure no thermal conduction between the reflector layers.
(b) Why is the MLI allowed to vent into space?
It is designed to withstand the harsh environment of the space and significantly aids in successful Space exploratory operations.
(c) Why are the layers grounded to the spacecraft?
The layers are grounded to the spacecraft to control and maintain acceptable temperatures on the spacecraft by acting as an insulator by using several radiation-heat transfer barriers to hinder energy flow.
Question 17
A spacecraft is going through the asteroid belt to the outer planets.
How much danger will it be in being destroyed by dust or small particles, a lot, a little, or negligible? Why?
There is little risk traversing through the asteroid belt. The asteroid belt contains four main asteroids; Ceres, Vesta, Pallas, and Hygiea while the remaining bodies range down to the size of a dust particle. The asteroid material is so lightly dispersed that many unmanaged spacecraft have crossed it without destruction.
References
Boato, M. G., Garcia, E. C., Santos, M. B., " Beloto, A. F. (2017). Assembly and Testing of a Thermal Control Component Developed in Brazil. Journal of Aerospace Technology and Management, 9(2). Retrieved from http://www.scielo.br/ scielo.php?script=sci_arttext"pid=S2175-91462017000200249
Decibel-Watt (dBW). Retrieved from https://www.rapidtables.com/electric/dBW.html.
Dooling, D. " Finckenor, M. M. (1999). Multilayer insulation materials guideline. Retrieved from https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990047691.pdf
Jain, R. (2015). Why are all satellites and missiles launched from the east coast? Retrieved from http://www.thehindu.com/sci-tech/science/why-are-all-satellites-and-missiles-launched- from-the-east-coast/article7202159.ece
Kawa, M. J. (2011). Fundamentals of active vs. passive thermal management. Retrieved from https://www.electronicproducts.com/Thermal_Management/Heat_Sinks_and_Thermal_ Materials/Fundamentals_of_active_vs_passive_thermal_management.aspx.
Martel, F., Pal, P. K., ITHACO, Inc., " Psiaki, M. (N.d). Active magnetic control system for gravity gradient stabilized spacecraft. https://pdfs.semanticscholar.org/1d12 /d41f75ddd9752f8c137d165ff62e3de7c6ac.pdf.
NASA. (2009). Apollo 13. Retrieved from https://www.nasa.gov/mission_pages/apollo /missions/apollo13.html
Radioisotope Thermoelectric Generators (RTGs). Retrieved from https://saturn.jpl.nasa.gov
Starin, S. R. (2018). Attitude Determination and Control Systems. Retrieved from https://ntrs.nasa.gov /archive/nasa/casi.ntrs.nasa.gov/20110007876.pdf
Why Are Rockets Launched From Areas Near The Equator? Retrieved from https://www.scienceabc.com/eyeopeners/why-are-rockets-launched-from-areas-near-the- equator.html
