Engineering topics

Kwok, Johnny H.

Publications and source records attributed to Kwok, Johnny H..

12 records

NASA NTRS2008

Mission Architecture and Technology Options for a Flagship Class Venus In Situ Mission

Venus, as part of the inner triad with Earth and Mars, represents an important exploration target if we want to learn more about solar system formation and evolution. Comparative planetology could also elucidate the differences between the past, present, and future of these three planets, and can help with the characterization of potential habitable zones in our solar system and, by extension, extrasolar systems. A long lived in situ Venus mission concept, called the Venus Mobile Explorer, was prominently featured in NASA's 2006 SSE Roadmap and supported in the community White Paper by the Venus Exploration Analysis Group (VEXAG). Long-lived in situ missions are expected to belong to the largest (Flagship) mission class, which would require both enabling and enhancing technologies beside mission architecture options. Furthermore, extreme environment mitigation technologies for Venus are considered long lead development items and are expected to require technology development through a dedicated program. To better understand programmatic and technology needs and the motivating science behind them, in this fiscal year (FY08) NASA is funding a Venus Flaghip class mission study, based on key science and technology drivers identified by a NASA appointed Venus Science and Technology Definition Team (STDT). These mission drivers are then assembled around a suitable mission architecture to further refine technology and cost elements. In this paper we will discuss the connection between the final mission architecture and the connected technology drivers from this NASA funded study, which - if funded - could enable a future Flagship class Venus mission and potentially drive a proposed Venus technology development program.

Balint, Tibor S.↗

NASA NTRS2008

Short- and Long-Term Propagation of Spacecraft Orbits

The Planetary Observer Planning Software (POPS) comprises four computer programs for use in designing orbits of spacecraft about planets. These programs are the Planetary Observer High Precision Orbit Propagator (POHOP), the Planetary Observer Long-Term Orbit Predictor (POLOP), the Planetary Observer Post Processor (POPP), and the Planetary Observer Plotting (POPLOT) program. POHOP and POLOP integrate the equations of motion to propagate an initial set of classical orbit elements to a future epoch. POHOP models shortterm (one revolution) orbital motion; POLOP averages out the short-term behavior but requires far less processing time than do older programs that perform long-term orbit propagations. POPP postprocesses the spacecraft ephemeris created by POHOP or POLOP (or optionally can use a less accurate internal ephemeris) to search for trajectory-related geometric events including, for example, rising or setting of a spacecraft as observed from a ground site. For each such event, POPP puts out such user-specified data as the time, elevation, and azimuth. POPLOT is a graphics program that plots data generated by POPP. POPLOT can plot orbit ground tracks on a world map and can produce a variety of summaries and generic ordinate-vs.-abscissa plots of any POPP data.

Smith, John C., Jr.↗

NASA NTRS2004

Spitzer Space Telescope mission design

This paper gives a description of the mission design, launch, orbit, and navigation results for the Spitzer space telescope mission. The Spitzer telescope was launched by the Delta II Heavy launch vehicle into a heliocentric Earth trailing orbit. This orbit is flown for the first time and will be used by several future astronomical missions such as Kepler, SIM, and LISA. This paper describes the launch strategy for a winter versus a summer launch and how it affects communications. It also describes how the solar orbit affects the design and operations of the Observatory. It describes the actual launch timeline, launch vehicle flight performance, and the long term behavior of the as flown orbit. It also provides the orbit knowledge from in-flight navigation data.

Mission Design↗

NASA NTRS1992

LOP - Long-Term Orbit Predictor

Long-Term Orbit Preditor (LOP) trajectory-propagation computer program is useful tool in analysis of lifetime of orbiting spacecraft. Suitable for studying planetary-orbit missions with reconnaissance (flyby) and exploratory (mapping) trajectories. Includes sample data for study of drift cycle of geosynchronous station, strategy for radar mapping of Venus, frozen orbit about Mars, and orbit characterized by repeating ground trace. Executed faster than such programs based on Cowell's method. Written in FORTRAN 77.

Kwok, Johnny H.↗

NASA NTRS1991

System requirements and design for the Space Infrared Telescope Facility (SIRTF)

The Space Infrared Telescope Facility (SIRTF) is the fourth in NASA's series of Great Observatories and will feature a one-meter class telescope in high earth orbit. Planned for launch around the turn of the century, the lifetime of this cryogenically cooled observatory will be approximately five years. This paper presents an overview of the current status of the requirements and design for SIRTF. This iterative process is described, and some examples are drawn from the upper end of the hierarchy.

Mclaughlin, William I.↗

NASA NTRS1991

Mission design for the Space Infrared Telescope Facility (SIRTF)

The Space Infrared Telescope Facility (SIRTF) is the fourth in NASA's series of Great Observatories. It will feature a one-meter class cryogenically cooled telescope. It is planned for a NASA fiscal start for the development phase in 1994 with a launch in about 2001. The launch vehicle will be the new upgraded Titan IV with a Centaur upper stage. The operational orbit will be circular at an altitude of about 100,000 km. The planned mission lifetime is 5 years. This paper addresses the rationale in the selection of the high altitude orbit, the performance of the launch vehicle in delivering the observatory to orbit, other orbit options, and the planned observational modes and capabilities of the observatory. The paper will also address the viewing geometry and viewing constraints affecting science observation, telescope aperture shade design, and spacecraft solar-panel and communication design.

Kwok, Johnny H.↗

NASA NTRS1990

Artificial Satellite Analysis Program (ASAP)

Program suited for studying planetary orbit missions including mapping and flyby components. Sample data included for geosynchronous station drift cycle study. Venus radar mapping strategy, frozen orbit about Mars, and repeat ground trace orbit. Written in FORTRAN.

Kwok, Johnny H.↗

NASA NTRS1990

Design of a Mars rover and sample return mission

The design of a Mars Rover Sample Return (MRSR) mission that satisfies scientific and human exploration precursor needs is described. Elements included in the design include an imaging rover that finds and certifies safe landing sites and maps rover traverse routes, a rover that operates the surface with an associated lander for delivery, and a Mars communications orbiter that allows full-time contact with surface elements. A graph of MRSR candidate launch vehice performances is presented.

Bourke, Roger D.↗

NASA NTRS1989

Artificial-Satellite-Analysis Program

Artificial Satellite Analysis Program (ASAP) is general orbit-predicting computer program incorporating sufficient orbit-modeling accuracy for design and planning of missions and analysis of maneuvers. Suitable for study of planetary-orbit missions with spacecraft trajectories of reconnaissance (flyby) and exploratory (mapping) nature. Not written for specific mission and intended use for almost any planetary orbiting mission. Written in FORTRAN 77.

Kwok, Johnny H.↗

NASA NTRS1989

Orbit design and perturbation analysis for Mars rover and sample return mission concepts

Mission options using out-of-orbit entry and Mars orbit rendezvous before earth return are discussed. The following major flight elements are required to conduct a Mars rover and sample return mission: the rover, the sample return orbiter, and the Mars ascent vehicle. The effects of perturbations on orbital motion are studied using Cowell's method and an averaging technique.

Kwok, Johnny H.↗

NASA NTRS1989

Mars Rover Sample Return mission

To gain a detailed understanding of the character of the planet Mars, it is necessary to send vehicle to the surface and return selected samples for intensive study in earth laboratories. Toward that end, studies have been underway for several years to determine the technically feasible means for exploring the surface and returning selected samples. This paper describes several MRSR mission concepts that have emerged from the most recent studies.

Bourke, Roger D.↗

NASA NTRS1989

Mars Rover and Sample Return Mission design

The current reference Mars Rover and Sample Return mission is described. Technical issues are outlined, including high-resolution image acquisition and reconstruction, approach navigation, ground and flight systems operational complexity, rover autonomy, autonomous rendezvous and docking in Mars orbit, aerocapture and aeromaneuver, estimating the probability of mission success, and end-to-end information system design. Focus is placed on lander hazard identification and avoidance, pinpoint landing guidance and control, Mars ascent vehicle guidance and control, planetary protection and quarantine, sample acquisition and preservation, project management and control, systems requirements and interface control, and costing. In addition, program issues such as international participation, fiscal constraints, and launch-vehicle availability are considered.

Kwok, Johnny H.↗