This document discusses various additive manufacturing techniques that could enable in-space manufacturing and addresses key parameters to consider. It suggests that vat photopolymerization using a two-photon approach may allow 3D printing of plastics and composites in space without gravity affecting the process. An alternative approach using a centrifuge module to provide artificial gravity is also proposed to allow stereolithography additive manufacturing in microgravity conditions. The document analyzes the technical feasibility and challenges of both approaches.

1. 1
Arvind Srinivasan Karthikeyan
Parameters to be considered for in-space manufacturing
 Vacuum of space
 Zero gravity
 Intense thermal fluctuations
 Extreme and harsh environmental
obstacles
 Cost
 Human oversight
 Consistent production quality
 Standardizing design software
 Equipment parameters
 Testing standard
 Understanding of material properties
in space and their structural
properties
Figure 1:Energy Consumption of different AM processes
Techniques
Sheet Lamination
 Possible to work under microgravity.
 With the tension from two of rolls on each side of the device.
 Does not need human interference to feed the stock. Can be automatically fed.
 Limited on type of materials and size of material.
Material Extrusion
 This method has already been employed for 3D printing in space.
 Ease of feeding the stock due to the solid form of filament and the size used was 1.75
mm.
 Offers good resolution of up
to 40 microns.
 It is cheap and the equipment
is light weight
 It has printing dimensions of
25 x 25 x 25 cm3
 Power consumption less than
100 W.
 But it has limitations on
materials since it cannot print
Teflon, PEEK or nanocomposites that are used in space and steps are also taken to
improve the layer resolution.
Figure 2:Layer thickness of FDMfabricated parts over different gravity

2. 2
Arvind Srinivasan Karthikeyan
VAT Photo polymerization
 Can be used for in-space manufacturing by modifying certain parameters to suit the
conditions prevalent is space.
 Size is not a constraint and this is the preferred method for polymers since the post
processing method is relatively simpler and pollution-free.
 Polymers could be recycled and used again. Makes a viable resource for repair spare
parts.
 Only constraint is to hold the liquid under gravity
Material Jetting
 They can be used for finding a suitable method to hold liquid under gravity. Similar to
VAT polymerization and major advantage of this method is producing multiple part
materials which are in heavy demand for in-situ fabrication.
 However, ability to not produce high strength and durability metal parts might be a
constraint so the probability of preferring this type is lower.
Powder Bed Fusion
 Can be used if a binder can be used to hold the powder together in a sheet and this sheet
could be fed continuously after a layer of sheet has already been cured. By doing this,
complication of powders spreading everywhere could be avoided.
 Implementation the above stated method is a huge challenge
Printing
Method
Plastic or
Metal
Zero Gravity
Capability
Vacuum
Compatibility
Materials
Min Layer
Thickness
BuildVolume Feasibility
Sheet
Lamination
Either High Yes
Paper, Plastic, Sheet
Metal
100 µ
21 x 25 x 40
cm3
High
Material
Extrusion
Plastics
Material
Dependent
Partial
ABS,
Polycarbonate, PC-
ABS
100 µ
25 x 25 x25
cm3
High
VAT Photo-
Polymeriza
tion
Plastics Low
Not by
conventional
methods
ABS,
Polycarbonate, PC-
ABS
50 µ
180 x 160 x
210 cm3
Medium
Material
Jetting
Plastics
Material
Dependent
No Wax and Plastics 16 µ
30 x 18.5 x 20
cm3
Low
Powder
Bed Fusion
Metals
and
Plastics
Low Yes
Metals, alloys,
polymers.
60-100 µ
55 x 55 x 75
cm3
Low
Table 1: Comparison of all method parameters

3. 3
Arvind Srinivasan Karthikeyan
Structural Application
We can observe that a major number of
failures associated with space travel is
with electrical & electronic
components and with Plastic and
Composite materials. Our choice of
application revolves around Plastics
and Composites as they make up over
a quarter of the total hardware failure;
also plastics and composites are
recyclable in nature. Since a lot of accessories in a space mission are made of plastic including
buckles, clams and containers; it becomes critical to ensure their renewability in-situ.
To tackle this, we propose use of VAT Photopolymerization technique with a Two Photon
approach for additive manufacturing of these Plastics and Composites.
Concept:
 The two-photon approach involves intersecting two separate arrays of photons in the
VAT filled with polymer. The 3-dimensional vector traced by this point of intersection
of the two arrays will form a solid material within the VAT.
 This allows us to hold a photopolymer liquid in a sealed transparent chamber without
any recoating or surfacing.
 The transparent chamber will consist of each an inlet and an outlet and a face plate.
 The face plate will be attached to the chamber; the outlet will depressurize the chamber
whilst keeping the inlet close. Once vacuum is achieved the inlet will be let open to
allow the photopolymer to be sucked inside the chamber.
 Two arrays of photon will cure the material as per the CAD file within the VAT.
 Once the part is completed the remaining resin is sucked out of the outlet.
 The chamber is repressurized and removed from the faceplate to expose the created part.
 This part can be further cured in a UV oven to achieve the desired properties.
This process is a minor tweak over the
conventional process of SLA. The incident
lights hold energy lower than the critical
energy required for photopolymerization.
The intersection where both lasers meet
collectively provide energy which exceeds
the critical energy and start curing the resin.
Figure 3: Representation of total failures in ISS by material type
Figure 4: Illustration of the proposed process

4. 4
Arvind Srinivasan Karthikeyan
An alternate approach to SLA in zero gravity could be made by artificially creating the effect
of gravitational pull.
This is acieved by making the machine experience centripital acceleration. The International
space station was intended to contain a Centrifuge Accomodations Module which could
provide controlled acceleration rates (artificial gravity) for experiments. Such a Module would
allow our SLA machine to function with very little modification to the actual design.
This setup however would pose a challenge as the liquid reservoir will not simply lie flat within
in its container while it is being spun out, the water surface will for a concentric arc to the path
of the spin. This concave shape of the liquid must be controlled, if it is too extreme the printer
won't behave correctly.
The figure to the right illustrates this situation. We can
calculate the difference in the heights of the concave
curvature by using trigonometry.
( 𝑅 − ∆ℎ)2
+ 𝑋2
= 𝑅2
Which can be rewritten as
∆ℎ = 𝑅 − √ 𝑅2 − 𝑋2
Taking
𝑅 = 1.25 𝑚 (The proposed capsule for ISS was 2.5 m)
𝑋 = 0.0625 𝑚 (The width of Form1 is 12.5cm)
From the data obtained in fugure 6 it is reasonable to assume
that if the printer is allowed to rotate at a radius of at least 0.7
meters, where the height difference between the fluid is less
than 3mm that the printer would be capable of operating in a micro-gravity setting.
These measures would
allow to manufacturing
of certain components
in space. However
these parts would be
subjected to further
scrutiny and testing.
Figure 5: Schematic representation of
Centrifuge Accommodations Module.
Figure 6: Fluid Height vs Radius of rotation from the given calculations.

5. 5
Arvind Srinivasan Karthikeyan
References
"Centrifuge Accommodations Module". En.wikipedia.org. N.p., 2016. Web. 28 Nov. 2016.
https://en.wikipedia.org/wiki/Centrifuge_Accommodations_Module
Glenn, Valerie D. "NTRS: NASA Technical Reports Server200695ntrs: NASA Technical
Reports Server. Washington, DC: National Aeronautics And Space Administration
1994‐ . Gratis Last Visited July 2005 URL: Http://Ntrs.Nasa.Gov/". Reference
Reviews 20.2 (2006): 40-41. Web.
Kopchak, Obadiah and View profile. "Can Stereo Lithography Printing Work In A
Microgravity Environment". Myspareideas.blogspot.com. N.p., 2016. Web. 23 Nov.
2016.
"Projects". Made In Space. N.p., 2016. Web. 22 Nov. 2016.
Richards, Louise M. "NASA Technical Reports Server (NTRS)2008364NASA Technical
Reports Server (NTRS). Washington, DC: NASA Center For Aerospace Information
Last Visited June 2008. Gratis URL: Http://Ntrs.Nasa.Gov/". Reference Reviews 22.8
(2008): 40-41. Web.
"Sheet Lamination | Additive Manufacturing Research Group | Loughborough
University". Lboro.ac.uk. N.p., 2016. Web. 24 Nov. 2016.
Ordway, Frederick I. and R. E. Street. "Advances In Space Science And Technology, Volume
3". Physics Today 15.3 (1962): 60. Web.
Lee, Kwang-Sup, et al. "Two-photon stereolithography." Journal of Nonlinear Optical
Physics & Materials 16.01 (2007): 59-73.
Wong, Julielynn Y., and Andreas C. Pfahnl. "3D printing of surgical instruments for long-
duration space missions." Aviation, space, and environmental medicine 85.7 (2014):
758-763.
Chandrasekhar, Prasanna, et al. "Variable emittance materials based on conducting polymers
for spacecraft thermal control." SPACE TECHNOLOGY AND APPLICATIONS INT.
FORUM-STAIF 2003: Conf. on Thermophysics in Microgravity; Commercial/Civil Next
Generation Space Transportation; Human Space Exploration; Symps. on Space Nuclear
Power and Propulsion (20th); Space Colonization (1st). Vol. 654. No. 1. AIP
Publishing, 2003.