In this class, we've talked about different types of space missions, with four of the primary categories being Navigation spacecraft, Observation spacecraft (which may look at the Earth or out into space), Communication spacecraft, and Exploration spacecraft.
In this assignment, you will work on your own to learn more about these systems in order to supplement the presentations made during lecture.
NAVIGATION - During lecture, we will spend little time discussing the ways that navigation satellites work. These questions and their references will introduce you to satellite navigation technology. You should definitely work your way through the outstanding Trimble Navigation's GPS Tutorial; additional references include the Wikipedia SatNav Overview, the Global Positioning System Overview, and the Wikipedia Overview of GPS. Other references are certainly available via the web.
1. First, you should certainly be aware that satellite-based navigation is only one method of navigation; many others exist and have been used for far longer. List three navigation methods that do not rely on spacecraft.
2. As for satellite navigation services, you are certainly aware of GPS. But there are others, and it is worth being aware of at least a little information about them:
3. The original operational GPS system used 24 satellites in 6 different orbital planes (although more satellites are now operational).
4. To quantitatively explore the concept of multi-lateration, let's do a few simple 2-D "bi-lateration" planar examples. Imagine that there are two signal sources, each broadcasting a signal that moves at 1 unit per second. One source is at the origin of the Cartesian plane, (0,0). The second source is at (10,0).
REMOTE SENSING - These questions relate to the phenomena, technologies and associated system sizing relationships for remote sensing missions. A primary reference for answering these questions is Section 11.2 of Understanding Space. Other references exist, of course, and you are encouraged to seek them out as necessary.
4. In the context of remote sensing, briefly explain the difference between a passive and an active sensing system.
5. How do high-performance infrared sensors drive the thermal design of a satellite, and why is this the case?
6. You have an option of putting your remote sensing satellite into either an LEO orbit (altitude of 600 km) or a geosynchronous orbit (altitude of about 35,800 km). At geosynchronous altitude, your camera system is capable of 10m resolution. What resolution would the same camera system achieve in the LEO orbit? Refer to Eq 11-8 in Understanding Space.
7. Many hot objects emit infrared energy and are interesting enough that we want to find and track them from space; things like forest fires, rocket plumes, etc. Given the information in the Sellers chapter as well as that from the thermal subsystem lectures about radiation, consider a object that is 1,000 deg C., and for the purposes of this problem assume that it is a perfect blackbody radiator. MIND YOUR UNITS!!!
8. Briefly describe how the design of a remote sensing system effects other subsystems for the following situations:
COMMUNICATION - The questions below relate to major design considerations when developing high power communication missions. Relevant references are noted below.
9. High power communications spacecraft need to generate a LOT of power, and they thermally dissipate a LOT of power. From the thermal perspective, consider a thermal balance for a spherical communication spacecraft with a 1 meter diameter in LEO. Following the white paint example shown on Slide 42 of the Thermal Subsystem lecture, the steady state temperature with 0W of internally dissipated power was -67 deg C.
10. The Link Equation, shown below, relates the quality of a communication link (in terms of signal to noise ratio) to many of the driving contributions such as broadcast power, antenna gain, losses over distance and through the atmosphere, etc.
More information on the Link Equation is found in the MECH 371 presentation supplement on this subject. There are many things to learn regarding where this equation comes from and how it is used in the design and analysis of communication systems. However, using this equation as a rough guide, we can determine some of the big trade-offs when it comes to designing a communications payload (as well as the communications subsystem for a satellite with a different payload).
SCIENCE - These questions relate to a generic planetary spacecraft, which for our purposes represents a "science class" satellite mission.
11. As with other spacecraft, the requirements and characteristics of planetary missions drive the design of the bus subsystems/components. For a generic planetary mission, consider how various subsystems of the planetary craft would differ significantly compared to those of a satellite designed for a low Earth orbiting mission.
For example, for propulsion (which we study in MECH 371), planetary spacecraft often require significant fuel and more substantial thrust systems (compared to an LEO mission) for achieving its interplanetary trajectory - this increases mass, requires thermal management, etc.
For each of the subsystems listed below, provide a few similar thoughts on the primary effects and considerations: