Correction: Future Mission Capabilities Enabled by an Evolved NTP Powered Space Launch System Exploration Upper Stage

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Future Mission Capabilities Enabled by an Evolved
NTP Powered Space Launch System Exploration Upper Stage
Arthur Beckman1, Benjamin Donahue2, David Burks2, Robert Loper2
Boeing Exploration Systems, Washington DC1 & Huntsville2, AL, USA
C. Russell Joyner3
L3Harris Technologies3, Jupiter, Florida, USA
Douglas R. Cooke4
Cooke Concepts and Solutions4, Gettysburg, PA, USA
James L. Green5
Space Science Endeavors5, Silver Spring, MD, USA
Justin Kasper6
BWX Technologies6, Washington DC, USA
James Reuter7
JLR Aerospace7, Washington DC, USA
Nuclear Thermal Propulsion (NTP) holds significant potential for deep space exploration, offering
critical advantages for robotic and human missions. Specific impulse performance of NTP systems are
nearly double that of the most chemically energetic combination of Liquid Oxygen (LO2) and Liquid
Hydrogen (LH2), significantly improving efficiency for in-space propulsion. This technology could
drastically reduce mission mass and transit time, two major challenges for all deep space exploration
missions. NTP is not a new concept and has been studied for decades. It was tested in the 1960s during
the NERVA program, proving the technology. NTP has long been studied for human Mars exploration
missions. In the concept presented here, the NTP stage would be evolved from the Space Launch
System (SLS) Exploration Upper Stage (EUS) which was designed for deep space operations. The NTP
EUS would leverage systems, structures, and the Hydrogen tank, from the current SLS/EUS, but
would replace conventional LOX/H2 RL10 engines with an NTP engine. A departure point launch
configuration for this paper includes an NTP stage which would be launched atop the SLS/EUS Block
II configuration, operating as a third stage, and once reaching a nuclear safe orbit (NSO), the nuclear
engine would be safely activated. The combination of SLS/EUS with an EUS derivative NTP stage
provides the advanced capabilities needed for efficient transportation to undertake deep space human
and robotic missions. This paper presents examples of robotic mission examples to highlight the value
of including NTP in future deep space launch vehicle architectures. While this paper focuses on the
important metric of mass delivered to various destinations, there are also trades between mass
delivered and transit times which will be explored in subsequent studies. With growing interest in
Mars and other deep space missions, now is the time to initiate preliminary design efforts of full scale
NTP systems to help clarify technical challenges and to include NTP capabilities in mission planning
scenarios for future deep space robotic and human exploration missions.
1. Nomenclature
CERMET = CERamic-METallic (Tungsten based alloy with Uranium Oxide or Uranium Nitride in a material matrix),
CERCER = CERamic- CERamic (Zirconia and Carbide with Uranium Oxide or Uranium Nitride in a material matrix),
DARPA = Defense Advanced Research Projects Agency, EUS = Exploration Upper Stage, HALEU= High Assay
Low Enriched Uranium (~19.75% U235), HEU=Highly Enriched Uranium (>90% U235), H2 = molecular hydrogen,
Isp = Specific Impulse, PBM = Power Balance Model (steady state model), LH2 = Liquid Hydrogen, LO2 = Liquid

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Oxygen, NASA = National Aeronautics and Space Administration, NERVA = Nuclear Engine for Rocket Vehicle
Applications, NSO = Nuclear Safe Orbit, NTP = Nuclear Thermal Propulsion, RCS = Reaction Control System, SLS
= Space Launch System, SNP= Space Nuclear Propulsion, T/W = Thrust to Weight.
2. Introduction
NASA, industry, and other government organizations have evolved NTP to use High-Assay Low Enriched Uranium
(HALEU) fuel elements that can advance the NTP technology for exploration missions. The HALEU, with a low
uranium content of 19.75% U235), is a nuclear fuel material that is capable of high temperature operation to achieve
high specific impulse (Isp) at or above 900 seconds. Fuel element temperatures between 2,800 to 3,000 Kelvin (K)
have been demonstrated in tests. This technology, when coupled with an existing large LH2 capacity upper stage can
significantly improve deep space exploration mission capability. An NTP design with a 25,000 lbf thrust level is
optimal for a variety of missions, including NASA crewed Mars missions. NASA and DARPA work has been looking
at thrust levels from 3,000 to 15,000 lbf and provide a path to subscale prototypes that could also be used in a flight
demonstration. The subscale prototype would present a smaller reactor, reduce any ground testing footprint, and could
use off-the-shelf technology, additively manufactured non-nuclear components to reduce cost. The smaller NTP
designs would also be attractive as a planetary escape stage for deep space missions.
While all other rockets, with the exception of the Apollo-era Saturn V rocket, have been designed for payload
delivery to Low Earth Orbit, the SLS was designed explicitly as a deep space exploration launch vehicle with emphasis
on maximizing volume and payload for trans-lunar injection in a single launch. Starting in 2027, the SLS will be
upgraded with an exploration class upper stage, the EUS, to take full advantage of the SLS core stage lift capabilities.
The SLS Block-1B configuration will offer mission performance capabilities which were abandoned with the
retirement of the Saturn V rocket in the 1970’s. Exploration and science both stand to benefit from the Block 1B, but
upgrading the only available deep space launch vehicle to include NTP will create a never before imagined capability.
Integrating NTP into the SLS EUS would allow SLS to accommodate heavier payloads, and shorter trip times,
significantly enhancing mission profiles compared to the current chemical propulsion stages. This evolution would be
a game-changer, not only for human exploration but also for deep space science missions, which are currently limited
by smaller rockets. NTP offers a revolutionary approach to Mars exploration by reducing mission mass, cutting transit
times, and enhancing mission safety compared to previous NTP systems using HEU fuel elements.
3. Nuclear Thermal Propulsion for the Evolved EUS Upper Stage
The early NASA Rover/NERVA NTP designs consisted of highly enriched uranium (HEU) (e.g., uranium metal
consisting of 93% by mass of U235 isotope) which used dispersed tie-tubes to support the fuel within the Engine core.
These early designs achieved very high power; the Rover core designs were rated at from 1100 to 5000 MWt. These
early designs were based on a specific matching of fuel and tie-tube material, for Rover, the combination was Uranium
fuel within a graphite matrix, where the graphite material, which held the fuel provided the moderation (slowing down)
of the fission neutrons to achieve adequate reactivity. The slowed neutrons are referred to as thermal neutrons, and
the benefit of reducing their velocity via the use of graphite material was to increase the likelihood of capture by a
Uranium nucleus. One of the last NTP engine systems tested was the PEWEE-1 design. The smaller PEWEE-1 core
(rated at 500 MWt), was moderated with ZrH (Zirconium Hydride) sections to achieve sufficient reactivity with a
smaller core size at minimum mass. The smaller PEWEE-1 design approach has been leveraged over the past twenty
years to examine both HEU and HALEU 500 MWt class power level NTP designs [1].
The newer, safer HALEU NTP has had considerable design work performed since 2019 after earlier 2016-2017
studies confirmed that HALEU NTP was technically feasible. Design work has included increasing fidelity cycle
analysis modeling, detailed mechanical design and integration, as well as components performance mapping.
Concurrently detailed nozzle design was conducted, which was tied to the legacy Aerojet Rocketdyne RL10C-2
LO2/LH2 engine configuration which has flown on the NASA SLS, and examination of the instrumentation and
control architecture.
The current NASA NTP studies have switched from the older NERVA-type moderator element approach with fuel
elements to the new HALEU configurations around 2019. The first fuel design focused on CERMET (ceramic
Metallic) (e.g., Uranium Nitride-Molybdenum Tungsten), moderator, configured as fuel assemblies. These were
optimized in loading and geometry to work with a cylindrical moderator block sandwiched between supports and
enclosed within a standard pressure vessel arrangement. Since 2019 other fuel materials have been studied such as
CERCER (Ceramic-Ceramic) (e.g., Uranium Nitride-Zirconium Carbide). The design process for HALEU NTP
studies has included detailed thermodynamic cycle analysis and has been documented in several published papers

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[2, 3, 4, 5, 6]. Fig. 1 [19] shows a simplified rocket thermal cycle; specifically, an expander cycle configuration
suitable for the 25,000 lbf thrust NTP.
Fig. 1: Example HALEU NTP Using RL10 Flight-Proven Expander Cycle
Engine Chamber pressures from 650 to 1,000 psia have been examined; the lower end pressure, 650 psia, is
similar to the flight-proven RL10. Fig. 2 shows the regeneratively cooled chamber-nozzle and radiatively cooled
nozzle design configuration permitting nozzle retraction like the legacy United Launch Alliance/Boeing Delta 4
RL10B-2 and the current NASA SLS RL10C-2. By retracting the nozzle for launch on the SLS the NTP stage can
be shorter. Once separated, the nozzle is extended to its full length.
Fig. 2: Full scale Chamber-Nozzle Contour for 900 sec Isp

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The HALEU 25,000-lbf thrust NTP configuration using either CERMET or CERCER fuel types provides an engine
thrust to weight (T/W) of 3:1, a lower thrust half-size NTP would have a slightly lower T/W as shown in Table 1.
These T/W’s do not include an external shield (shield mass estimates are 1,000 kg for human missions and about half
that for robotic missions depending on the proximity of the payload to the NTP). If the NTP length is greater than 10-
m and separated from the payload with propellant tank and structure the radiation shielding mass could be lower. This
is accomplished by using targeted “spot-shielding” on radiation sensitive components.
TABLE 1. Full Scale and Subscale NTP Engine Data.
Parameter
Full Scale
NTP Engine
Subscale
NTP Engine
Thrust
25,000 lbf
12,500 lbf
T/W
2.9
1.4
Design Isp
900-910 sec
900-905 sec
Fig. 3 [19] provides a depiction of a 25,000-lbf thrust HALEU NTP with a retractable nozzle section to reduce the
NTP length on the launch vehicle. Assuming this engine length and a similar sized LH2 tank as EUS, the overall NTP
stage is approximately the same size as the conventional EUS, resulting in a launch vehicle stack height of
approximately 320 ft. Considering the constraint of the VAB external door height, this configuration allows for a 90
ft payload fairing to clear the upper door opening. Fig. 4 shows a comparison of the Block 1B SLS crew configuration
to a NTP cargo configuration in relation to the VAB door.
Fig. 3: HALEU NTP Engine System Components Integration Based on CAD Model.

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Fig. 4: Comparison of SLS Block 1 with NTP Configuration.
4. NTP Performance Benefits
NTP technology has the capability to transform the high energy mission category with its superior Isp of 900
seconds—twice the capability of the traditional cryogenic LO2/LH2-fueled rocket engines, with an Isp of 460 seconds,
currently the state of the art for rocket engine efficiency. This advancement in propulsion efficiency would benefit
missions by reducing the required size for large, crewed mission Mars-bound spacecraft in half. NTP's ability to
shorten mission trip times, offer protection for astronauts by significantly reducing their in-space time and exposure
to natural gamma radiation. Fig. 5 illustrates the benefits of NTP reduced Mars one-way mission trip times vs chemical
propulsion. synodic planetary alignment cycle [7, 8, 9, 10].

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Fig. 5: NTP Reduces Human Mars One-way Trip Time Compared to Chemical Stage.
Fig. 6 from NASA Design Reference Architecture [5] also illustrates the reduction in mission time NTP can
provide for human Mars missions versus nuclear electric, solar electric and chemical propulsion. Reducing Mars trip
time increases the mission delta-velocity (dV) and the higher Isp of NTP provides additional margin to reduce the
trip time before the mass of the vehicle begins to increase rapidly due to the increased propellant requirements. Fig.
6 has a lower and upper region to the trade space to show how Earth-Mars trajectories significantly vary across the
15-year synodic planetary alignment cycle [11].
Fig. 6: NASA B. Drake Webinar Mars Challenges 2013 – Propulsion Architecture Trades.
NTP's current design prioritizes environmental stewardship. The NTP reactor is launched cold—unactivated—
eliminating the risk of radioactive contamination during launch. While crewed Mars missions would gain considerably
from NTP's capabilities, incorporating NTP into future robotic exploration missions within the SLS architecture would
yield significantly higher payload capacities or shorter travel times to planetary destinations [12, 13, 14, 15].

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5. The Exploration Upper Stage (EUS), The Departure Point for a NTP Stage
The EUS is the largest Liquid Oxygen (LO2) / Liquid Hydrogen (LH2) upper stage ever produced, with a propellant
loading (114-mt, 248,000-lbm). The first EUS flight unit will be available in 2027 for the Artemis IV mission. With
an 8.4-m diameter fairing above it, the EUS can accommodate very large diameter spacecraft and offers new
opportunities to simplify spacecraft design. The SLS EUS is propelled by four LO2/LH2 RL10 engines; these engines
operate with Isp of 460 seconds. The stage pictured in Fig. 7, includes LH2 and LO2 tanks, feedlines, valves and
pressurization systems to feed the RL10 engines. The EUS also includes computers, two-way communication and
control avionics, power systems and a Reaction Control System (RCS) for precise in-space maneuvering. The EUS
is essentially a self-contained space vehicle which can be controlled, and docked to other space systems in a real time
manner depending upon the mission requirements. The stage is built at NASA’s Michoud Assembly Facility (MAF)
alongside the SLS Core stage, which is also a LO2/LH2 system. In addition to sharing the same assembly facility, the
SLS EUS and Core stage share tooling, personnel, certification and test processes.
Fig. 7: The Baseline EUS Chemical Propulsion Stage.
6. The Uprated NTP EUS: Common Systems Used
The EUS, currently in final development, is an excellent departure point for a deep space NTP derivative stage as it
was designed to perform extended missions in deep space. The EUS pedigree also includes NASA’s human rating
design rigor and has been designed to be tolerant of deep space environments including radiation.
The majority of systems in the EUS can be directly leveraged to efficiently evolve to an NTP transfer stage, including
a very large LH2 tank which holds up to 40,000 lbm (18.4 mt) of Hydrogen. With NTP using LH2 as the primary
working fluid, the existing EUS LH2 tanks and feed systems will all be applicable. Additionally, SLS propellant tanks
are built in a modular fashion and can be easily shortened or stretched depending upon stage optimization. From a
manufacturing perspective the EUS NTP derivative could be built in the same facility as SLS and EUS using much of
the same tooling, personnel and certification processes. Changes to the present EUS stage would entail removal of the
LO2 tank and its feedlines, the RL10 engines, along with some modification of the vehicle structure. Additions to the
EUS stage would consist of adding: 1) the new NTP engine and 2) a radiation shield.
Fig. 8: Nuclear Thermal Propulsion EUS Derivative Stage.
The NTP engine uses a single propellant (coolant): Hydrogen; and the radiation shield is a single piece disk of dense
Tungsten material (with no moving parts) that is located just forward of the NTP engine. The shield absorbs the high
energy gamma rays that are generated by the NTP reactor. The EUS NTP derivative stage shown in Fig. 8, would
provide a marked benefit to high energy missions; Isp is a significant factor in a stage’s performance capability; the
NTP stage, with an Isp about twice that of the present RL10 EUS stage (910 sec vs 460 sec) would greatly enhance
many deep space missions and enable several very high energy missions that are presently not feasible with chemical
propulsion systems. Because the EUS presently has a very large diameter (8.4 m) LH2 holding 18.4 mt of LH2, its

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present LH2 tankage, feed and pressurization system could be used with little modification to accommodate the LH2
NTP engine. All Hydrogen systems presently utilized on the current EUS would be applicable (with little modification)
to the uprated NTP stage. The current avionics, power, RCS, control, pressurization and telemetry systems will all be
retained for the NTP stage to allow for commonality and cost saving in development, certification and testing. Since
the NTP derivative stage would have a smaller thrust level than the present four RL10 EUS, structural loads would be
less, and well within the capabilities of the current stage systems. By removing all the LO2 systems, some
simplification will be achieved for the stage, at least forward of the NTP engine.
7. The NTP EUS Stage: Flight Operations for One-Way Mission Trips
After launch on the SLS, The EUS NTP stage with its payload would be placed in a Nuclear Safe Orbit (NSO >1800
km). The standard LO2/LH2 EUS stage is used to boost the NTP stage to its starting NSO orbit. Once there, the now
empty LO2/LH2 standard EUS is jettisoned. The NTP EUS is then turned on. The reactor control drums, that are
located outside of, and around the reactor, are turned such that their neutron reflector sides of the rods are facing the
reactor. Only then can the reactor startup via the initiation of fission. From NSO the NTP EUS boosts its payload out
of Earth orbit into its Heliocentric transfer trajectory. Once the NTP stage has made the injection, the stage separates
from the payload. The NTP reactors control rods are turned back, such that the neutron absorbing side of the rods are
facing the reactor. The fission process can no longer continue, and the reactor shuts down. A small amount of LH2 is
retained in the tank to provide some post-shut down cooling of the reactor, this Hydrogen is released out of the reactor
through the nozzle. The reactor’s total mission burn time will be on the order of several minutes. After the stage is
jettisoned, it will have imparted sufficient velocity to the spacecraft for it to arrive at its destination. Because of the
stages' very high Isp, the NTP stage is considerably more efficient than chemical stages at injecting large spacecraft
to deep space destinations. After the jettison of the NTP stage it will have no further Earth Interaction. This flight
operational approach does not require the long-term cryogenic LH2 storage technology that will be needed for a
roundtrip Mars human mission, allowing NASA an early return on its investments in NTP technology.
8. Performance Benefits of the Very High Specific Impulse NTP EUS Stage
The benefits of very high Isp reach to many exploration missions; in this paper four Design Reference Missions
(DRM) are presented that clearly illustrate the significant advantage that an NTP EUS stage can provide.
8.1 DRM 1: Fast Transfer Uranus Orbiter Mission
The first mission to be discussed is the launch of a Uranus orbiter into a very fast, short trip time transfer of 7 years
[16]. To accomplish this, a high injection energy of 91-km2/s2 is required. High Isp propulsion provides the most
benefit when high energy missions are selected; this Uranus mission was selected for that purpose. The SLS Block 2,
with the standard RL10 EUS, will inject the evolved NTP EUS to the NSO. From there, the NTP stage can inject a
14.3-mt spacecraft into the 7-year trajectory. This compares to an all chemical solution (without the NTP stage) which
can inject a 6.8-mt spacecraft to the same 7-year trajectory. Use of the NTP stage more than doubles the payload mass
injected to Uranus. A significant increase in mass capability provides tremendous flexibility in payload design and
creates opportunities for international participation by carrying other mission elements such as probes as shown in
Table 2. This result is representative for fast transfers to other outer planet destinations, including Saturn, Neptune
and Pluto.
Table 2: Uranus Mission Engine Comparison
Uranus Fast-Transfer
Mission
Chemical Stage
NTP Stage
Comment
Mass delivered on
7-year trajectory
6.8 mt
14.3 mt
210% Increased
8.2 DRM 2: Pluto Orbiter Mission
Launched in 2006, the 487 kg New Horizons spacecraft successfully flew past Pluto and its large moon Charon in
2015. Despite the great advances made possible by the New Horizons mission, many aspects of the Pluto system
remain difficult to understand based on the tantalizing observations that could be collected in the days around the
flyby. A follow-on orbiter mission to Pluto would produce transformative discoveries. A future Pluto orbiter will
reveal the geology and composition of the remaining ∼60% of Pluto and Charon that were not mapped in detail by
New Horizons and allow how Pluto’s atmosphere and surface change with time [17]. The second DRM is the launch
of a spacecraft into a 9.5-year transfer to Pluto leading to an orbiter. The all chemical solution (ORION-50X solid

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upper stage on top of the standard RL10 EUS) can inject a 2.7-mt spacecraft to the same 9.5-year trajectory; however,
2.7-mt would not allow sufficient propellant to achieve a later propulsive capture into an orbit about Pluto while
retaining a reasonably sized orbiter. To accomplish this, not only is a high injection energy (157.8-km2/s2) required,
but also a propulsive capture into orbit from a very high (14-km/s) Pluto arrival velocity would be required of the
spacecraft. For this mission the SLS Block 2 with the standard EUS will inject the evolved NTP EUS to NSO; which
from there can inject an 8.2-mt spacecraft into the 9.5-year trajectory. This 8.2-mt mass allows for the spacecraft to
carry sufficient propellant to decelerate and capture the spacecraft into an elliptical orbit about Pluto as shown in Table
3. The NTP EUS therefore, enables a significant Pluto orbiter mission to be accomplished.
Table 3: Pluto Mission Engine Comparison.
Pluto Orbiter Mission
Chemical Stage
NTP Stage
Comment
Mass delivered on
9.5-year trajectory
2.7 mt
(insufficient fuel for orbit)
8.2 mt
304% Increase
8.3 DRM 3: Interstellar Explorer Mission – to the Heliopause in 15 years
The third DRM evaluated is the interstellar Probe mission [16, 18]. To reach beyond the Heliopause in 15 years
would require an incredibly high injection energy, C3=304 km2/s2. This would be the fastest spacecraft ever launched.
The NTP’s very high Isp is especially advantageous to this mission. Again, the SLS Block 2, with the standard RL10
EUS, will inject the evolved NTP EUS to the NSO. From there, the NTP stage can inject a 1.4-mt spacecraft into the
Interstellar trajectory. This compares to an all chemical solution (which uses an ORION-50X solid upper stage on top
of the standard RL10 EUS), which can inject a 0.18-mt spacecraft to the same trajectory. Use of the NTP stage provides
an order-of-magnitude increase in the payload that can be injected into the 15-year trip to the edge of the solar system
as shown in Table 4.
Table 4: Interstellar Probe Mission Engine Comparison.
Interstellar Probe
Mission
Chemical Stage
NTP Stage
Comment
Mass delivered on
15-year trajectory
0.18 mt
1.4 mt
77,778% Increase
8.4 DRM 4: Mars Cargo Mission
The fourth DRM evaluated is an uncrewed Mars cargo mission. Here the SLS is used to inject heavy payloads
directly into a 9-month trajectory to Mars; injection energy, C3=12.0 km2/s2, represents an average year opportunity
in the 15-year Earth-Mars synodical cycle. After injecting to NSO, the NTP stage can inject 36.8-mt to Mars. This
compares to 31.5-mt, which the SLS Block 2/ RL10 EUS can launch without the NTP stage. Use of the NTP stage
provides a significant increase (5.3-mt) in payload. Table 5 provides the comparison.
Table 5: Mars Cargo Mission Engine Comparison.
Mars Cargo Mission
Chemical Stage
NTP Stage
Comment
Mass delivered on
9-month trajectory
31.5 mt
36.8 mt
17% Increase
9. Other Nuclear Thermal Propulsion Considerations
NTP transfer stages with high Isp operation and high thrust flight offer a viable option for exploration missions,
especially those requiring high energy. Other NTP considerations for space exploration missions include:
1. Technology Maturity. Nuclear thermal engines have been demonstrated extensively in ground test; several
development engines were tested during the joint Los Alamos Scientific Lab and NASA project ROVER and
NERVA programs. Separate reactor fuel element tests have been conducted on a variety of configurations and
material combinations. Liquid hydrogen (LH2) pumps are a mature technology as well. Engine restart has been
demonstrated in ground tests. Fail safe reactor control systems (typically control drums) have been demonstrated,

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as have radiation hardened engine components. The NASA Von Braun Mars mission planning team of the late
1960’s anticipated NTP based propulsion systems to be best suited for high energy crewed Mars missions. Long
term (months-to-years) in-space storage of LH2 without significant boiloff remains a significant challenge with
technology maturation underway to address. The flight operations approach presented in Section 7 for the one-
way missions discussed in Section 8 greatly reduces the need for long-term LH2 storage (to days-and-weeks).
This enables an evolutionary approach to addressing this challenge, allowing very long term LH2 in-space storage
technology to be deferred until two-way humans-to/from Mars are implemented.
2. Simplicity. An advantage of NTP systems is their operational simplicity. NTP systems do not require the
mixture of two propellants for combustion. The NTP system uses a single cooling fluid (typically LH2) that is
heated in the reactor; the hot H2 gas is exhausted out of the nozzle producing thrust. Many fuel elements are used
in the reactor and the loss of a few elements would reduce slightly the exhaust temperature of the H2 gas slightly
but not substantially change the operation of the engine. Very high specific impulse (Isp) can be achieved at
modest chamber pressure (Pc); 900 psia would be typical. Reactor radiation shielding requires no moving parts;
shielding is provided by a Tungsten plate at the forward end of the engine. The NTP reactor can be launched
without any buildup of fission products; appreciable fission product buildup would not occur until after the vehicle
is beyond Earth escape velocity; and beyond any later Earth interaction.
10. Conclusion
NTP offers the potential to revolutionize human and scientific exploration of Mars and beyond by increasing
payload capacities and reducing mission transit times thereby addressing several critical challenges associated with
deep space missions. In this paper we developed conceptual designs to better understand the challenges and path ahead
that could be greatly facilitated by NTP implanted with the EUS system within the SLS.
NASA and DARPA are at the forefront of this pioneering effort to leverage nuclear propulsion for space
maneuvering. This transformative technology overcomes the constraints of chemical rockets, offering significant
opportunities to shorten travel times to Mars and beyond and/or trade travel times against additional delivered mass.
NTP systems offer the versatility of delivering either high thrust, akin to chemical rockets, or paired with electric
propulsion in a bimodal architecture to provide sustained power and thrust. When a bimodal architecture is
implemented, NTP provides substantial power—over 50 kilowatts-electric (kWe)—for spacecraft systems. Bimodal
configurations are also another area for further analysis.
Boeing’s visionary look to the future recognizes the advantages of utilizing NTP for human Mars missions are
flexible and vary with each mission's design. NTP can deliver additional mass and/or faster transit times over
traditional chemical propulsion, allowing for large delta-Vs to Mars and other destinations. Use of the NTP stage on
SLS can greatly enhance and even enable future planetary missions.
The implications of nuclear propulsion are profound, potentially leading to more frequent missions, larger payloads,
and the viability of establishing human outposts well beyond cis-lunar space. While the development and deployment
of nuclear propulsion involve substantial and known technical challenges, the aim is to expand our horizons as a space-
faring civilization.
In essence, nuclear propulsion is about taking bold and visionary strides into the future of space exploration. A large-
scale NTP capability offers the next opportunity to dramatically accelerate our learning and understanding of the
universe. With NASA's ongoing work on the SLS and advancements in nuclear propulsion and power, we are moving
toward a future where distant celestial bodies become reachable destinations in an expansive interplanetary network.
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