Engineering topics

Onoufrios Theofylaktos

Publications and source records attributed to Onoufrios Theofylaktos.

6 records

NASA NTRS2022

Titan In-situ Resource Utilization (ISRU) Sample Return (TISR)

Titan is unique in the outer solar system in that it is the only moon with a thick atmosphere, and the only body in the solar system outside the Earth with liquid seas on its surface. The Titanian oceans, however, are seas of liquid hydrocarbons, and the rocks on the surface are solid water ice. Like other icy Moons of the outer solar system, beneath the ice crust, Titan also has a subsurface ocean. Rodriguez et al. refer to it as the “world with two oceans”, an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. [1] Titan is scientifically fascinating in many ways [2], [3], [4]. The Compass Team will emphasize just one here: Titan is a high priority target for astrobiology [4] [5] [6] [7] [8] [9] [10] [11]. It is a world with a surface and atmosphere rich in the complex organic compounds known as tholins. A detailed understanding of the nature of these complex compounds will require an analysis using a full laboratory on Earth. Because of its value to understanding the organic compounds of the outer solar system which may be the primordial building-blocks of life, return of samples from Titan to laboratories on Earth will be the primary goal of this mission. While this would give unprecedented science return, returning even a small sample from Titan using conventional technology would be tremendously difficult. Saturn is almost a billion miles from the Earth, about thirteen times farther than Mars. A return mission to Saturn requires such a large total-mission ∆V that, with conventional technology, the mass ratios required are prohibitive. Such a sample return would truly be “mission incredible.” But to date, a sample return mission from so distant a target has been assumed to be, not merely incredible, but mission impossible. The Compass Team has proposed [2] [12] that by manufacturing the propellant for the return to Earth using the resources available on Titan, such a mission becomes possible. The task of this report is to show that it is reasonable with credible space technology.

Titan↗

NASA NTRS2022

Dynamic Radioisotope Power System (DRPS) Design Reference Mission (DRM) Lunar Rover

The Radioisotope Power Systems (RPS) Program tasked the Compass Team to evaluate use of Dynamic Radioisotope Power Systems (DRPS) for lunar science rovers. The object was to identify their advantages and challenges as well as to influence the technology developments with flight-type requirements. This was easily done by using the promising Volatiles Investigating Polar Exploration Rover (VIPER) solar- powered rover mission as a platform to ‘swap in’ a DRPS. The ‘pickup truck bed’ approach allowed both simplified installation and operation of the DRPS while keeping the forward lunar surface ‘blocked’ from the DRPS waste heat which could sublimate the icy surface. It was found that with the Stirling DRPS option the mass is within the planned VIPER lander capability and is very close to VIPER mass and size (the DRPS replaces large battery pack/solar arrays). The Stirling DRPS option produced ~300 Watts electrical (We) using six general purpose heat source (GPHS) bricks and eight Stirling convertors. Replacing the solar/battery power with radioisotope power allows a continuous presence (instead of 6 hours) in a permanently shadowed region (PSR) and over 18 months of operations with minimal science impact (rearward surface heating). It was also found that use of a dynamic system (instead of a thermoelectric system) reduces the heat impact on the science environment two-to-three times. The DRPS, along with a relay link (like Gateway), can provide continuous access to PSRs. The system was also found to be capable of roving for 8 hours per day with a range of over 500 km in 18 months. Preliminary cost estimates fit into a Class D mission but only assuming VIPER heritage and launch, lander, operations, nuclear specific costs [National Environmental Policy Act (NEPA), fueling, transport, Launch Services Program (LSP), etc.] and DRPS are not included.

DRPS↗

NASA NTRS2021

Compass Final Report: Nuclear Electric Propulsion (NEP)-Chemical Vehicle 1.2

Many previous studies have examined sending crews to and from Mars. The most economical involved a ‘conjunction’ class whereby the crew spends around 500 days on Mars waiting for a ‘cheap’ return. The total mission time results in over a 1000-day mission duration (about 3 years). Given the current experience level of only one year on the International Space Station (ISS), it of interest to reduce that time to only two years, thus reducing risk and minimizing required Mars surface infrastructure. The Phase 1.1 Study goal was stated as follows, “Determine the feasibility of a two-year roundtrip class Mars mission concept of operation that enables boots on Mars no later than 2036.” While the Phase1 study did show feasibility for the NEP-Chemical option, the 2036 Opposition opportunity was found to stress the schedule due to proposed technology development schedules. A 2039 Opposition (which requires even more energy than the 2036 case) was chosen as representative for Phase 1.2. Phase 1.2 also sought to further refine the concept, building on the feasibility, but addressing several challenges brought by the red team and habitat team. Given the date of 2039, nearer term technologies, primarily nuclear thermal and nuclear electric were deemed as the most viable for these missions. As will be shown, the energy required to perform such a mission in only two years (for the 2039 opportunity at least) is about three times that of the three-year conjunction mission. The rocket equation shows that this mission would then require several times the propellant of the three-year mission unless the specific impulse (ISP) of the propulsion system can be increased. Based on lunar needs, a limit of five Space Launch System (SLS) launchers with 8.4m fairings was imposed for the piloted transportation portion of the mission, limiting the size of the system. When using nuclear electric propulsion, the main limiting factor was packaging the required radiator area. The higher Isp nuclear electric propulsion (NEP) system option is described herein but with a twist: in order to keep the size of radiators packageable in one SLS and use proven reactor power system technology (~1200K reactor outlet temperature and superalloy-class Brayton) the NEP system had to be combined with a chemical propulsion system. This combination of electric propulsion and high thrust chemical was found to be useful in previous design studies combining solar electric propulsion (SEP) and chemical propulsion. Such a combination allowed the low-thrust system to provide significant change in velocity (∆V) during the interplanetary portions of the mission, thereby notably reducing the ∆V required by the high thrust system to capture and depart from the Mars gravity well. Here the high thrust ‘impulsive’ system is more efficient due to the Oberth Effect. A plethora of trades, both at the mission and system level, as well as the subsystem level were performed to develop these vehicle concepts. An entire family of NEP-Chemical transportation vehicles is described herein. The main driver and the primary focus was the piloted vehicle but additional concepts for cargo were performed using the same ‘building blocks’ in order to reduce costs and provide commonality.

Nuclear Power↗

NASA NTRS2021

Dynamic Radioisotope Power System (DRPS) Permanently Shadowed Region (PSR) Demonstrator Rover

This conceptual design study investigated trading several Dynamic Radioisotope Power Systems (DRPS) in development to supply power to a lunar science rover which operates for long periods (months) in permanently shadowed regions (PSR) over many years. The design was conducted by the Compass team and relied heavily on the planned VIPER rover design, which is limited to only a few hours of operations in PSRs and less than a month near the south pole. As such this conceptual design shows what a DRPS can do for a follow-on type VIPER rover. In addition to the long duration, go anywhere DRPS power system, the Compass team added a communications system that utilizes the Gateway spacecraft as a relay node for nearly 24/7 communications link to the DRPS rover in lunar craters not visible from the earth. The Compass design includes a notional conops, launch and delivery, subsystem designs of power, mobility, structures, science, command and data handling, communications, guidance and control, and thermal. The thermal design was especially important due the low temperatures in PSRs where the science environment needs to be shielded from the waste heat from the DRPS.

Dynamic Radioisotope Power Systems↗

NASA NTRSDate not supplied

Use of a Dynamic Radioisotope Power Source for a Long Duration Lunar Science Rover

The Radioisotope Power Systems (RPS) Program tasked the Compass Team to evaluate use of Dynamic Radioisotope Power Sources (DRPS) for lunar science rovers. The object was to identify their advantages and challenges as well as to influence the technology developments with flight-type requirements. This was done by using the promising Volatiles Investigating Polar Exploration Rover (VIPER) solar-powered rover mission as a platform to ‘swap in’ a DRPS. The resulting design used a ‘pickup truck bed’ approach which allowed simplified installation and operation of the DRPS while also keeping the forward lunar surface ‘blocked’ from the DRPS waste heat, which could sublimate the icy surface. It was found that with the Stirling DRPS option the mass is within the planned VIPER lander capability and is comparable to VIPER mass and size (the DRPS replaces large battery pack/solar arrays). The Stirling DRPS option produced ~300 Watts electrical (We) using six general purpose heat source (GPHS) bricks and eight Stirling convertors. Replacing the solar/battery power with radioisotope power allows a continuous presence (instead of six hours) in a permanently shadowed region (PSR) and over 18 months of operations with minimal science impact (rearward surface heating). It was also found that use of a dynamic system, instead of a thermoelectric system, reduces the heat impact on the science environment two-to-three times while still providing sufficient waste heat for the rover systems in the PSR (~ -200°C). The DRPS, along with a relay link (like Gateway), can provide extended access to PSR. The system was also found to be capable of roving for eight hours per day with a range of well over 100 km in 18 months.

Radioisotope Power↗

NASA NTRSDate not supplied

1.9 MWe Nuclear Electric Propulsion-Chemical Propulsion Piloted Mars Opposition Vehicle

To assess ‘quick’ missions to Mars, a study was performed to determine the feasibility of a two-year roundtrip class mission concept of operation that enables boots on Mars in the 2030s. After performing a Phase 1.1 2036 Mars opposition design case, the more difficult 2039 opposition design was pursued. This Phase 1.2 also sought to further refine the concept, building on feasibility, and addressing several challenges brought by independent team reviews. Given the date of 2039, nearer-term technologies, primarily nuclear thermal and nuclear electric were deemed as the most viable for these missions. This paper explores a nuclear electric and chemical combined propulsion approach to achieve the desired mission timeline.

Nuclear Electric Propulsion↗